Hologram recording/reproducing method and hologram recording/reproducing device

ABSTRACT

A method for holographic recording and reproducing includes a recording process and a reproducing process. In the recording process, a coherent reference beam is spatially modulated in accordance with information to be recorded to generate a signal beam, and the signal beam is converged. The converged signal beam enters and passes through a recording medium made of a photosensitive material. A diffraction grating area according to a light interference pattern is created in a portion where a 0th-order beam and a diffraction beam of the signal beam interfere with each other inside the recording medium. In the reproducing process, a reproduced wave corresponding to the signal beam is generated by illuminating the diffraction grating area with the reference beam.

TECHNICAL FIELD

The present invention relates to a recording medium made of aphotosensitive material, so-called a holographic memory, and especiallythe present invention relates to a method for holographic recording andreproducing and an optical information recording and reproducingapparatus using the holographic memory.

BACKGROUND ART

A volume holographic recording system is known as a digital datarecording system using a principle of holography. This system ischaracterized in that information is recorded on a recording medium madeof a photosensitive material such as a photorefractive material as avariation of a refractive index of the medium.

One of conventional methods for holographic recording and reproducinguses the Fourier transform for recording and reproducing.

Referring to FIG. 1, in the conventional 4f series of holographicrecording and reproducing apparatus, a beam splitter 13 splits a laserbeam 12 generated from a laser light source 11 into light beams 12 a and12 b. A beam expander BX expands the diameter of the light beam 12 a.Then, the light beam 12 a being a parallel pencil is applied to aspatial light modulator SLM such as the panel of a transmissive TFTliquid crystal display (LCD) and the like. The spatial light modulatorSLM receives information to be recorded as electronic signals encoded byan encoder, to form two-dimensional data, that is, a light and dark dotpattern and the like corresponding to the information formed on a plane.When the light beam 12 a passes through the spatial light modulator SLM,the spatial light modulator SLM optically modulates the light beam 12 ato a signal beam including a data signal component. Since the signalbeam 12 a including a dot pattern signal component passes through aFourier transform lens 16 disposed at a distance of a focal length ffrom the spatial light modulator SLM, the dot pattern signal componentis transformed to a Fourier component and converged into a recordingmedium 10. A light beam 12 b split by the beam splitter 13 is led intothe recording medium 10 with mirrors 18 and 19. The light beam 12 b as areference beam intersects the light path of the signal beam 12 a insidethe recording medium 10. The interference of the light beam 12 b and thesignal beam 12 a creates a light interference pattern. The whole lightinterference pattern is recorded as a diffraction grating such as thevariation of a refractive index (a refractive index grating) and thelike.

As described above, the coherent parallel pencil is diffracted by thedot pattern data, and forms an optical image with the Fourier transformlens. The distribution of the image on the focal plane of the Fouriertransform lens, namely on a Fourier plane, interferes with the coherentreference beam. Then, interference fringes are recorded on the recordingmedium in the vicinity of a focal point. After finishing the record of afirst page, the turnable mirror is turned by predetermined degrees andmoved in parallel, in order to vary the incident angle of the referencebeam 12 b into the recording medium 10. Then, a second page is recordedfollowing the same procedure as above. Multiple angle recording iscarried out in this way.

On the other hand, the inverse Fourier transform is used in reproducinga dot pattern image. In reproducing the recorded information, as shownin FIG. 1, the spatial light modulator SLM, for example, intercepts thelight path of the signal beam 12 a, so that only the reference beam 12 bis incident on the recording medium 10. The position and the angle ofthe mirror are so controlled by varying the combination of rotation andmovement thereof, that the incident angle of the reference beam 12 bbecomes same as that in recording of the page to be reproduced. Areproduced beam which reproduces the recorded signal beam appears on theopposite side of the recording medium 10, on which the recorded signalbeam 12 a is incident. Leading the reproduced beam to an inverse Fouriertransform lens 16 a and performing the inverse Fourier transformreproduces the dot pattern signals. The dot pattern signals are receivedby a photo detector 20 such as a charge-coupled device CCD and the likedisposed in the position of a focal length of the lens 16 a, andre-converted into the electrical digital data signals. Then, the digitaldata signals are sent to a decoder to decode original data.

Referring to FIG. 1, the multiple images are conventionally recorded ina few millimeters volume of the recording medium with the use ofmultiple angles and multiple wavelengths, in order to record theinformation in some volume thereof in high density. Accordingly, a widefield and long range coherent for the signal beam and the reference beamis necessary to secure the selectivity of an angle and a wavelength.Therefore, the intensity of the light beam per the amount of light usedfor recording is decreased. Multiple recording is necessary for highdensity recording, so that the recording medium which has a largeerasure time constant and is easy to perform the multiple recording isrequired.

The conventional holographic recording and reproducing apparatusrequires high spec two lenses, which are the Fourier transform lens andthe inverse Fourier transform lens. The apparatus also needs to beprovided with a high accuracy paging control mechanism for controllingthe reference beam in recording and reproducing the information.Therefore, there is a disadvantage that the apparatus becomes large insize.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a method forholographic recording and reproducing and an apparatus therefor whichcan decrease in size and record a hologram on a holographic recordingmedium.

According to the present invention, there is provided a method forholographic recording and reproducing comprising a recording process anda reproducing process,

-   -   the recording process including the steps of:    -   generating a signal beam by spatially modulating a coherent        reference beam in accordance with information to be recorded;    -   illuminating with the signal beam a recording medium made of a        photosensitive material to allow the signal beam to pass through        said recording medium; and    -   creating a diffraction grating area recorded by a light        interference pattern in a portion where a 0th-order beam and a        diffraction beam of the signal beam interfere with each other        inside said recording medium; and    -   the reproducing process including the step of:    -   illuminating said diffraction grating area with said reference        beam to generate a reproduced wave corresponding to the signal        beam.

The signal beam is a light beam resulted from such operation that acoherent reference beam spatially modulated in accordance withinformation to be recorded, which comprises a 0th-order beam having awavefront having the same shape wherever regardless spatial modulation;and a diffraction beam subjected to the spatial modulation. Thus, thepresent invention uses the 0th-order beam of the signal beam asreference light for a holographic recording.

In recording, the recording medium is illuminated with the signal beamto generate optical interference fringe patterns caused by the 0th-orderbeam and the diffraction beam at the path of the signal beam to recordthe refractive index grating in the recording medium correspondingly tothe interference fringe patterns.

In reproducing, the recording medium particularly the refractive indexgrating therein is illuminated with a signal beam which is not spatiallymodulated i.e., non-modulated reference beam with the same positionaland angular condition of the signal beam used in the recording. Sincethe non-modulated reference beam includes the 0th-order beam as a majorcomponents, the illumination of the non-modulated reference beam to therefractive index grating of the recording medium generates a reproducedwave having a wavefront as the same as that of the signal beam used inthe recording.

In a detection of the reproduced wave, the reproduced waves emitted fromthe refractive index grating in the recording medium overlap with thenon-modulated reference beam used for the reproducing. Removing orreducing the non-modulated reference beam used for the reproducingfacilitates to detect the reproduced wave easily and reproduce therecorded information electrically.

According to the present invention, there is also provided a recordingmedium made of a photosensitive material capable of being recorded byillumination with a coherent light beam, the recording medium comprisingan incident-light-processing area provided in said recording medium onan opposite side of an entrance surface of the recording medium on whichthe light beam is incident, the incident-light-processing areaseparating a 0th-order beam and a diffraction beam of the light beamfrom each other to return a part of the incident beam to the inside ofsaid recording medium.

To removing or reduce the non-modulated reference beam used for thereproducing, as shown in FIG. 2, the recording medium 10 is providedwith an incident-light-processing area R which comprises a0th-order-beam-processing area R1 processing the 0th-order beam of thesignal beam and the non-modulated reference beam and adiffraction-beam-processing area R2 processing the diffraction beam ofthe signal beam in such a manner that the incident-light-processing areais disposed at a beam waist of the non-modulated reference beam which isconverged by a condenser lens to focus on the opposite side of anentrance surface of the recording medium on which the beam is incident.

There are considered the use of a phase conjugate wave as one of methodsfor a holographic recording and reproducing system in the recording andreproducing method. The reproducing method with the phase conjugate beamgenerally requires the identical reference beam in both the recordingand reproducing similarly to the other methods. For example, there is amethod for recording and reproducing information in which the refractiveindex grating is generated and recorded by interference in the recordingmedium in such a manner that the signal beam is irradiate to therecording medium and reflected by a mirror to generate a phase conjugatewave back to the recording medium so that the phase conjugate wave andthe signal beam interfere each other. In such recording and reproducingmethod, there are drawbacks such as a necessity to insert and detach thereflecting mirror, a degradation of light source with a return of thesignal beam particularly the 0th-order beam, and a large-sized deviceincluding an optical systems to prevent the return light. In contrast,according to the present invention, the incident-light-processing areadissolves the problems because the 0th-order beam and the diffractionbeam in the incident light are processed individually with differentprocessed such as a separation to return a part of the incident beam tothe inside of the recording medium.

In addition, there is no necessity to provide respective two opticalsystems for the reference beam and signal beam differently than theconventional holographic recording and reproducing method in the presentinvention. Furthermore, the method of the present invention does notrequire a condenser lens with a high performance which is used as anobjective lens and the like. Adopting this recording and reproducingmethod is highly effective to simplify and miniaturize a recording andreproducing apparatus, because of using the 0th-order beam and thediffraction beam (spatially modulated in accordance with information tobe recorded) included in the signal beam.

According to the present invention, there is further provided a methodfor holographic recording comprising the steps of:

-   -   generating a signal beam by spatially modulating a coherent        reference beam in accordance with information to be recorded;    -   illuminating with the signal beam a recording medium made of a        photosensitive material to allow the signal beam to pass through        said recording medium; and    -   creating a diffraction grating area recorded by a light        interference pattern in a portion where a 0th-order beam and a        diffraction beam of the signal beam interfere with each other        inside said recording medium.

According to the present invention, there is still further provided amethod for holographic reproducing comprising the steps of:

-   -   providing a recording medium made of a photosensitive material        having a diffraction grating area formed through a recording        process including the steps of: generating a signal beam by        spatially modulating a coherent reference beam in accordance        with information to be recorded; and illuminating with the        signal beam the recording medium to allow the signal beam to        pass through said recording medium so as to form the diffraction        grating area recorded by a light interference pattern in a        portion where a 0th-order beam and a diffraction beam of the        signal beam interfere with each other inside said recording        medium; and    -   illuminating a coherent reference beam to the diffraction        grating area to generate a reproduced wave corresponding to the        signal beam.

According to the present invention, moreover there is provided aholographic recording and reproducing apparatus for recordinginformation as a diffraction grating area in a recording medium, and forreproducing said recorded information from said diffraction gratingarea, said holographic recording and reproducing apparatus comprising:

-   -   a holding section for detachably holding a recording medium made        of a photosensitive material;    -   a light source for generating a coherent reference beam,    -   a signal beam generating unit including a spatial light        modulator, said spatial light modulator spatially modulating        said reference beam in accordance with said information to be        recorded to generate a signal beam;    -   an interference unit including an illuminating optical system        for illuminating the recording medium with the signal beam to        allow it to enter into and pass through said recording medium,        said illuminating optical system creating a diffraction grating        area according to a light interference pattern in a portion        where a 0th-order beam and a diffraction beam of the signal beam        interfere with each other inside said recording medium, and said        illuminating optical system illuminating said diffraction        grating area with said reference beam to generate a reproduced        wave corresponding to the signal beam; and    -   a detecting unit for detecting said recorded information formed        into an image by the reproduced wave.

According to the present invention, there is also provided a holographicrecording apparatus for recording information as a diffraction gratingarea in a recording medium, comprising:

-   -   a holding section for detachably holding a recording medium made        of a photosensitive material;    -   a light source for generating a coherent reference beam;    -   a signal beam generating unit including a spatial light        modulator, said spatial light modulator spatially modulating        said reference beam in accordance with said information to be        recorded to generate a signal beam; and    -   an interference unit including an illuminating optical system        for illuminating the recording medium with the signal beam to        allow it to enter into and pass through said recording medium,        said illuminating optical system creating a diffraction grating        area according to a light interference pattern in a portion        where a 0th-order beam and a diffraction beam of the signal beam        interfere with each other inside said recording medium.

According to the present invention, there is furthermore provided aholographic reproducing apparatus for reproducing information recordedas a diffraction grating area in a recording medium, the reproducingapparatus comprising:

-   -   a holding section for detachably holding a recording medium made        of a photosensitive material;    -   a light source for generating a coherent reference beam;    -   an illuminating unit including an illuminating optical system        for illuminating the recording medium with the reference beam to        allow it to enter into and pass through the diffraction grating        area in the recording medium to generate a reproduced wave        corresponding to the signal beam; and    -   a detecting unit for detecting said recorded information formed        into an image by the reproduced wave.

According to the present invention, there is furthermore providedanother holographic recording and reproducing apparatus for recordinginformation as a diffraction grating area in a recording medium, and forreproducing said recorded information from said diffraction gratingarea, said holographic recording and reproducing apparatus comprising:

-   -   a holding section for detachably holding a recording medium made        of a photosensitive material;    -   a light source for generating a coherent reference beam;    -   a signal beam generating unit including a spatial light        modulator, said spatial light modulator spatially modulating        said reference beam in accordance with said information to be        recorded to generate a signal beam;    -   an interference unit including an illuminating optical system        for illuminating the recording medium with the signal beam to        allow it to enter into and pass through said recording medium,        said illuminating optical system creating a diffraction grating        area according to a light interference pattern in a portion        where a 0th-order beam and a diffraction beam of the signal beam        interfere with each other inside said recording medium, and said        illuminating optical system illuminating said diffraction        grating area with said reference beam to generate a reproduced        wave corresponding to the signal beam;    -   an incident-light-processing area provided in said recording        medium on an opposite side of an entrance surface of the        recording medium on which the signal beam is incident, the        incident-light-processing area separating the 0th-order beam and        the diffraction beam from each other to return a part of the        incident beam to the inside of said recording medium; and    -   a detecting unit for detecting said recorded information formed        into an image by the reproduced wave.

According to the present invention, there is also provided anotherholographic recording apparatus for recording information as adiffraction grating area in a recording medium, comprising:

-   -   a holding section for detachably holding a recording medium made        of a photosensitive material;    -   a light source for generating a coherent reference beam;    -   a signal beam generating unit including a spatial light        modulator, said spatial light modulator spatially modulating        said reference beam in accordance with said information to be        recorded to generate a signal beam;    -   an interference unit including an illuminating optical system        for illuminating the recording medium with the signal beam to        allow it to enter into and pass through said recording medium,        said illuminating optical system creating a diffraction grating        area according to a light interference pattern in a portion        where a 0th-order beam and a diffraction beam of the signal beam        interfere with each other inside said recording medium; and    -   an incident-light-processing area provided in said recording        medium on an opposite side of an entrance surface of the        recording medium on which the signal beam is incident, the        incident-light-processing area separating the 0th-order beam and        the diffraction beam from each other to return a part of the        incident beam to the inside of said recording medium.

According to the present invention, there is further provided anotherholographic reproducing apparatus for reproducing information recordedas a diffraction grating area in a recording medium, the reproducingapparatus comprising:

-   -   a holding section for detachably holding a recording medium made        of a photosensitive material;    -   a light source for generating a coherent reference beam;    -   an illuminating unit including an illuminating optical system        for illuminating the recording medium with the reference beam to        allow it to enter into and pass through the diffraction grating        area in the recording medium to generate a reproduced wave        corresponding to the signal beam;    -   an incident-light-processing area provided in said recording        medium on an opposite side of an entrance surface of the        recording medium on which the signal beam is incident, the        incident-light-processing area separating the 0th-order beam and        the diffraction beam from each other to return a part of the        incident beam to the inside of said recording medium; and    -   a detecting unit for detecting said recorded information formed        into an image by the reproduced wave.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the configuration of a conventionalholographic recording and reproducing system.

FIG. 2 is a schematic sectional view of a holographic recording mediumaccording to an embodiment of the present invention.

FIG. 3 is a schematic view showing the configuration of a holographicrecording and reproducing apparatus according to an embodiment of thepresent invention.

FIG. 4 is a schematic sectional view for explaining the recordingprocess carried out by the holographic recording and reproducingapparatus according to the embodiment of the present invention.

FIG. 5 is a schematic sectional view of a holographic recording mediumfor use in the embodiment of the present invention.

FIG. 6 is a schematic plan view for explaining the relation between theholographic recording medium and a spatial light modulator according tothe embodiment of the present invention.

FIG. 7 is a schematic perspective view for explaining the recordingprocess carried out by the holographic recording and reproducingapparatus according to the present invention.

FIG. 8 is a schematic sectional view for explaining the reproducingprocess carried out by the holographic recording and reproducingapparatus according to the embodiment of the present invention.

FIGS. 9 and 10 are schematic sectional views for explaining therecording process carried out by the holographic recording andreproducing apparatus according to modified examples of the embodimentof the present invention.

FIG. 11 is a schematic view showing the configuration of a holographicrecording and reproducing apparatus according to another embodiment ofthe present invention.

FIG. 12 is a schematic sectional view for explaining the recordingprocess carried out by the holographic recording and reproducingapparatus according to the embodiment of the present invention.

FIG. 13 is a schematic sectional view of a holographic recording mediumfor use in the embodiment of the present invention.

FIG. 14 is a schematic sectional view for explaining the reproducingprocess carried out by the holographic recording and reproducingapparatus according to the embodiment of the present invention.

FIGS. 15 to 17 are schematic sectional views for explaining therecording process carried out by the holographic recording andreproducing apparatus according to modified examples of the embodimentof the present invention.

FIG. 18 is a schematic view showing the configuration of a holographicrecording and reproducing apparatus according to another embodiment ofthe present invention.

FIG. 19 is a schematic plan view for explaining the relation between theholographic recording medium and a spatial light modulator according tothe embodiment of the present invention.

FIG. 20 is a schematic perspective view for explaining the recordingprocess carried out by the holographic recording and reproducingapparatus according to the present invention.

FIGS. 21 and 22 are schematic sectional views for explaining therecording process carried out by the holographic recording andreproducing apparatus according to modified examples of the otherembodiment of the present invention.

FIG. 23 is a schematic view showing the configuration of a holographicrecording and reproducing apparatus according to another embodiment ofthe present invention.

FIGS. 24 to 26 are schematic sectional views for explaining therecording process carried out by the holographic recording andreproducing apparatus according to modified examples of the otherembodiments of the present invention.

FIG. 27 is a schematic perspective view showing a device for anincident-light-processing area of a holographic recording andreproducing apparatus according to another embodiment of the presentinvention.

FIG. 28 is a schematic perspective view showing a recording mediumcartridge of a holographic recording and reproducing apparatus accordingto another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be hereinafter described withreference to the accompanying drawings.

The present embodiment does not use the reference beam provided byanother optical path in recording. Instead, only the signal beam isincident on the recording medium, and a refractive index gratinggenerated by interference between the 0th-order beam and the diffractionbeam of the signal beam is recorded. After that, the reproduced wave isreproduced from the refractive index grating by illuminating therefractive index grating only with the reference beam. Anincident-light-processing area is integrally provided in the recordingmedium on an opposite side of an entrance surface thereof on which thelight beam is incident. The incident-light-processing area separates a0th-order beam and a diffraction beam of the light beam from each otherto return a part of the incident beam to the inside of the recordingmedium.

First Embodiment

FIG. 3 shows a holographic recording and reproducing apparatus accordingto an embodiment. In the apparatus, a near-infrared laser like a DBR(Distributed Bragg Reflector) laser with a wavelength of 850 nm, forexample, is used as a light source 11. A shutter SHs, a beam expanderBX, a spatial light modulator SLM, a beam splitter 15, and a condenserlens 160 are disposed in the optical path of a reference beam 12. Theshutter SHs, controlled by a controller 32, controls an illuminationtime of the recording medium with light beam.

The beam expander BX expands the diameter of the light beam 12 passingthrough the shutter SHs. The light beam 12 becoming a parallel pencil isincident on the spatial light modulator SLM. The spatial light modulatorSLM displays light and dark dot matrix signals, in accordance withelectronic data received from an encoder 25. The electronic data isrepresented as a series of a page unit corresponding to atwo-dimensional page. Upon passing through the spatial light modulatorSLM on which the data is displayed, the reference beam is opticallymodulated into a signal beam 12 a including the data as a dot matrixcomponent. The condenser lens 160 performs the Fourier transform on thedot matrix component of the signal beam 12 a passing through the beamsplitter 15, and converges it so that the signal beam 12 a comes into afocus behind a mounted recording medium 10. When the shutter SHs isopened, the signal beam 12 a or the reference beam 12 is incident on theprincipal surface of the recording medium 10 at a predetermined incidentangle, a zero-degree for example, due to the condenser lens 160. Thebeam splitter 15 is a splitting unit to separate a reproduced wave(described later) from the optical path of the reference beam to supplyit the photo detector 20 of a photoelectric transfer device like a CCD.The spatial light modulator SLM and the CCD 20 are disposed at the focalpoint of the condenser lens 160.

In addition, the beam splitter 15 is disposed in such a position as tobe able to send the reproduced wave to the CCD 20. The CCD 20 isconnected to a decoder 26. The decoder 26 is connected to the controller32. Taking a case where information corresponding to the type of aphotorefractive crystal is attached to the recording medium 10 inadvance, when the recording medium 10 is mounted on a movable stage 60,which is a holding section to move the recording medium 10, thecontroller 32 automatically reads the information with a proper sensorto perform controllings of the movement of the recording medium 10 andthe recording and reprocusing adapted to the recording medium 10.

Referring to FIG. 3, the recording medium 10 is integrally provided onthe opposite side of an entrance surface with anincident-light-processing area R which includes a0th-order-beam-processing area R1 for passing the 0th-order beam in thesignal beam 12 a and a diffraction-beam-processing area R2 forreflecting the diffraction beam in the signal beam 12 a. Theincident-light-processing area R is provided for processing the signalbeam. For example, the incident-light-processing area R comprises anopening for passing the 0th-order beam, and thediffraction-beam-processing area R2 for defining the opening. Theincident-light-processing area R is not limited to above, as long as the0th-order-beam-processing area R1 has a different role than thediffraction-beam-processing area R2. Zeroth-order beam absorbingmaterial may be provided for the 0th-order-beam-processing area R1instead of the opening. In other words, the 0th-order-beam-processingarea R1 in the incident-light-processing area R passes or absorbs the0th-order beam.

The operation in a recording process will be hereinafter described.

The controller 32 shown in FIG. 3 controls the position of the movablestage 60 holding the recording medium 10 so that the objective recordingmedium 10 is moved to a predetermined recording position.

Then, the recording signals are sent from the encoder 25 to the spatiallight modulator SLM, and the spatial light modulator SLM displays aspecific pattern corresponding to data to be recorded.

Then, the shutter SHs is opened, and the spatial light modulator SLM isilluminated with a reference beam 12. A signal beam 12 a is generated inthe reference beam 12 spatially modulated by the spatial light modulatorSLM on which the pattern is displayed in accordance with information tobe recorded. The recording medium 10 is irradiated with the generatedsignal beam 12 a to the to start the recording process.

The recording process of the refractive index grating using the signalbeam 12 a (i.e., 0th-order beam and diffract ion beam therein) in therecording medium will be hereinafter described in detail.

As shown in FIG. 4, the signal beam 12 a includes a 0th-order beam and adiffraction beam subjected to the spatial modulation. The 0th-order beamof the signal beam 12 a has a wavefront having a constant shape withoutany influence from the spatial modulation and therefore it is referredto as “hologram-reference beam”. The diffraction beam of the signal beam12 a subjected to the spatial modulation is referred to as“hologram-signal beam”. Accordingly, the signal beam 12 a comprises thehologram-reference beam and the hologram-signal beam at least inrecording.

Since the recording medium 10 is illuminated with the signal beam 12 a,the hologram-reference beam and the hologram-signal beam are opticallyinterfered with each other to create an optical interference fringepattern P1, so that a refractive index grating P1 is recorded in therecording medium 10 due to the photorefractive effect.

The 0th-order beam (i.e., hologram-reference beam) of the signal beam 12a passes through the 0th-order-beam-processing area R1 of theincident-light-processing area R and goes out from the opposite side ofthe recording medium 10, on which the signal beam 12 a is incident. Thediffraction beam (i.e., hologram-signal beam) of the signal beam 12 a isreflected by the diffraction-beam-processing area R2 of theincident-light-processing area R back to the recording medium 10.Therefore such diffraction beam of the signal beam 12 a reflected by thediffraction-beam-processing area R2 is referred to as“reflected-hologram-signal beam”.

The reflected-hologram-signal beam and the hologram-reference beam areoptically interfered with each other in the recording medium 10 tocreate an optical interference fringe pattern P2, so that a refractiveindex grating P2 is recorded corresponding to the optical interferencefringe pattern P2 in the recording medium 10 due to the photorefractiveeffect.

In this way, the 0th-order beam and the diffraction beam (i.e., thesignal beam 12 a) from the spatial light modulator SLM together with thereflected diffraction beam from the diffraction-beam-processing area R2create the set of the three-dimensional interference patterns inside therecording medium 10 in the recording. As shown in FIG. 5, the refractiveindex gratings P1, P2 corresponding to optical interference fringepatterns P1, P2 are hologram-recorded in the recording medium 10 due toa photorefractive effect.

After recording of the recording medium 10, the shutter SHs is closed bycontrol of the controller 32.

When the recording is finished at the predetermined recording positionof the recording medium 10, the recording medium 10 is forced to move(in a “y” direction of FIG. 3) for the purpose of reaching anotherpredetermined recording position of the signal beam 12 a with respect tothe recording medium 10. Then a next recording is carried out followingthe previous procedure. The recording is sequentially carried out likethis.

FIG. 6 shows the recording medium 10 and the spatial light modulator SLMplaced side by side, which are viewed on an optical axis of the signalbeam 12 a in the direction from the light source. The0th-order-beam-processing area R1 of the incident-light-processing areaR provided in the recording medium 10 on the opposite side of theentrance surface defines a track TR which functions as the openingthrough which the 0th-order beam of the signal beam 12 a can mainlypass, as shown in FIG. 6. The track TR continuously extends to a “y”direction of FIG. 6. A plurality of tracks TR may be intermittentlyprovided in a line-like form. In this case, the tracks TR can hold apositional information of the 0th-order-beam-processing area R1 in therecording medium 10.

The recording medium 10 and the spatial light modulator SLM arerelatively disposed with respect to the optical axis in such a mannerthat the extending direction D_(TR) of the track TR makes apredetermined angle of θ (θ≠0) with the extending direction D_(SLM) of arow in the pixel matrix of the spatial light modulator SLM. Otherwisethe extending direction of a column of the spatial light modulator SLMpixel matrix may be used for the angle setting between the recordingmedium 10 and the spatial light modulator SLM. The reason for thisconfiguration of the angle setting between the recording medium 10 andthe spatial light modulator SLM is as follows.

Generally, the spatial light modulator SLM displays a two-dimensionaldot pattern whether or not to allow light to pass through each pixelbased on information to be recorded during recording. The spatial lightmodulator SLM spatially modulates the reference beam 12 passingtherethrough to generate the signal beam 12 a. Then, the Fouriertransform lens or condenser lens 160 performs the Fourier transform onthe signal beam 12 a to illuminate the recording medium 10 and to formon a Fourier plane FF a dot image caused by the 0th order beam anddiffraction beam.

As shown in FIG. 7, the highest frequency component in the signal beam12 a modulated by the spatial light modulator SLM is that corresponds tothe diffraction on the basis of pixel matrix (pitch is “a”) thereof. Thesignal beam 12 a is Fourier-transformed through the condenser lens 160and then the spectrum distribution of light intensity with respect to aspatial frequency appears on the Fourier plane FF, as shown in FIG. 7,according to the spatial modulation due to the spatial light modulatorSLM.

When using the spatial frequency (1/a) based on the pixel pitch of thespatial light modulator SLM, the wavelength (λ) of the signal beam 12 aand the focal length (f) of the Fourier transfer lens (condenser lens160), then the distance (d1) between the 0th-order beam and the1st-order diffraction beam on the Fourier plane FF can be expressed asfollows: d1=(1/a)·(λ)·(f). Taking a case where, for example, the spatiallight modulator having the pixel dot pitch of 10 μm, the wavelength ofthe signal beam 12 a is 530 nm and the focal length is 14 mm, thedistance (d1) between the 0th-order beam and the 1st-order diffractionbeam is approximately 750 μm, according to the above equation. Since thehighest frequency component in the signal beam 12 a modulated by thespatial light modulator SLM that corresponds to the pixel matrix pitch,dot images corresponding to such pixel matrix pitch appear at positionsfarthest from the dot image caused by the 0th order beam of the signalbeam 12 a on a Fourier plane FF. Therefore, on the Fourier plane FF, themost part of the spectrum distribution of spatial frequency caused bythe spatial light modulator resides within the area which centers on the0th-order beam of the signal beam 12 a and is delineated by the1st-order diffraction beams that correspond to the pixel pitches alongthe row and column directions in the the spatial light modulator SLM.

The dot image caused by the diffraction beam corresponding to theextending direction Ds of a row of the spatial light modulator SLM pixelmatrix is included in the incident-light-processing area R in theFourier plane FF. When the extending direction D_(TR) of the track TRmakes an angle θ=0 with the extending direction D_(SLM) of a row in thepixel matrix of the spatial light modulator SLM with respect to theoptical axis of the signal beam intersecting them, the dot imagecorresponding to a spatial frequency component in the row extendingdirection D_(SLM) of the spatial light modulator SLM falls on the trackTR.

Therefore the diffraction beam corresponding to the row extendingdirection D_(SLM) of the spatial light modulator SLM is not reflected bythe diffraction-beam-processing area R2. Accordingly, there is noreflected-hologram-signal beam (corresponding to the row extendingdirection D_(SLM) of the spatial light modulator SLM) originated fromthe signal beam 12 a in the generation of the optical interferencefringe pattern P2 above-mentioned, so that no optical interferenceoccurs with the hologram-reference beam of the signal beam 12 a. Inother words, when the extending direction D_(TR) of the track TR makesan angle θ=0 with the extending direction D_(SLM) of a row in the pixelmatrix of the spatial light modulator SLM with respect to the opticalaxis of the signal beam intersecting them, any information based on thediffraction beam corresponding to the row extending direction of thespatial light modulator SLM is not recorded in the refractive indexgrating P2 of the recording medium 10.

The low frequency component of information to be recorded concentratesin the vicinity of the 0th-order beam, but the 0th-order beam is passedthrough on purpose. This embodiment uses the remaining diffraction beamwhich appears at points around the 0th-order beam.

In order to effectively use the diffraction beam, namely to opticallyinterfere the reflected-hologram-signal beam of the signal beam 12 a(corresponding to the row extending direction of the spatial lightmodulator SLM) with the 0th-order beam of the signal beam 12 a (i.e.,hologram-reference beam), the recording medium 10 and the spatial lightmodulator SLM are relatively disposed with respect to the optical axisin such a manner that the extending direction D_(TR) of the track TRmakes a predetermined angle θ (θ≠0) with the extending direction D_(SLM)of a row (or a column) of the spatial light modulator SLM pixel matrix.

The operation in a reproducing process will be hereinafter described.

The controller 32 controls the position of the movable stage 60 holdingthe recording medium 10, as shown in FIG. 3, so that the objectiverecording medium 10 is moved to the predetermined recording position.

Then, in order not to modulate a reference beam 12 spatially modulatedby the spatial light modulator SLM, the information which changes allpixels into a transparent state is sent from the encoder 25 to thespatial light modulator SLM, and the spatial light modulator SLMdisplays a transparent pattern.

Then, the shutter SHs is opened, and the spatial light modulator SLM isilluminated with reference beam 12 to generate a signal beam 12 a. Thenthe recording medium 10 is illuminated with the signal beam 12 a. Inthis way, the reproducing is started. It is noted that the signal beam12 a is not spatially modulated during the reproducing process becausethe spatial light modulator SLM displays the transparent pattern.Therefore no diffraction beam due to the spatial modulation occurs andthus the signal beam 12 a includes only the 0th-order beam (i.e.,hologram-reference beam).

The reproducing process of the refractive index grating using the signalbeam 12 a (i.e., hologram-reference beam) in the recording medium 10will be hereinafter described.

As shown in FIG. 8, the recording medium 10 is illuminated with a signalbeam 12 a (which is not spatially modulated i.e., hologram-referencebeam) with the same positional and angular condition of the signal beamused in the recording. Just then, the refractive index gratings P1 andP2 are illuminated with the signal beam 12 a in the recording medium 10,so that there emanate a first reproduced wave from the refractive indexgrating P1 corresponding to the recorded information and a secondreproduced wave from the refractive index grating P2 respectively. Thesignal beam 12 a passing through the 0th-order-beam-processing area R1goes out from the opposite side of the entrance surface of the recordingmedium 10 on which the beam is incident. Therefore, the signal beam 12 adoes not return to the condenser lens 160 nor reach the photo detector20. This phenomenon contributes to simplification of the reproducing ofthe recorded information.

The first reproduced wave is reflected back by thediffraction-beam-processing area R2 of the incident-light-processingarea R to the recording medium 10 and goes out from the entrance surfaceof the recording medium 10 and passes through the condenser lens 160.The second reproduced wave, being originated from the diffractiongrating recorded with the light reflected by thediffraction-beam-processing area R2 in the recording process, goes outfrom the entrance surface of the recording medium 10 and passes throughthe condenser lens 160. In this way, at least the first and secondreproduced waves go out from the entrance surface of the recordingmedium 10 and pass through the condenser lens 160.

After passing through the condenser lens 160, the first and secondreproduced waves are reflected by the beam splitter 15 and form an imagedot pattern corresponding to the recorded information on the photodetector 20. Then the photoreceptor of the CCD 20 receives it tore-convert its dot pattern signals into the electrical digital datasignals. Then, the digital data signals are sent to the decoder 26 toreproduce the original data.

Next the shutter SHs is closed by control of the controller 32, afterreproducing of the recording information at the predetermined recordingposition.

Next the recording medium 10 is forced to move (in a “y” direction ofFIG. 3) for the purpose of reaching another predetermined recordingposition of the signal beam 12 a with respect to the recording medium10. Then a next reproducing is carried out following the previousprocedure. The reproducing is sequentially carried out like this.

Second Embodiment

FIG. 9 shows another modified example of the embodiment. Anincident-light-processing area R comprises thediffraction-beam-processing area R2 provided in the recording medium 10on the opposite side of the entrance surface, and a0th-order-beam-scattering area SC provided inside the recording medium10 along a track. The 0th-order-beam-scattering area SC functions asanother 0th-order-beam-processing area R1 which separates the 0th-orderbeam of the incident light from the diffraction beam thereof and returnsa part of the beam to the inside of the recording medium 10. The0th-order-beam-scattering area SC scatters the 0th-order beam of thesignal beam 12 a. The track-shaped 0th-order-beam-scattering area SCextending in the “y” direction sends the 0th-order beam of the signalbeam 12 a back into the recording medium 10. The holographic recordingis carried out with the use of the interference fringes created from thescattered 0th-order beam, the incident 0th-order beam, the incidentdiffraction beam and the reflected diffraction beam.

In other words, the incident-light-processing area R of the recordingmedium 10 comprises a 0th-order-beam-scattering area SC scattering the0th-order beam of the signal beam 12 a (i.e., hologram-reference beam)and a diffraction-beam-processing area R2 reflecting the diffractionbeam (i.e., hologram-signal beam). The 0th-order-beam-scattering area SCcontinuously extends to a “y” direction of FIG. 9 like a track. Aplurality of 0th-order-beam-scattering areas SC may be intermittentlyprovided in a line-like form. In this case, the0th-order-beam-scattering areas SC can hold a positional information ofthe 0th-order-beam-processing area R1 in the recording medium 10.

The recording process of the refractive index grating using the signalbeam 12 a (i.e., hologram-reference beam and hologram-signal beam) inthe recording medium will be hereinafter described.

Since the recording medium 10 is illuminated with the signal beam 12 a,the hologram-reference beam and the hologram-signal beam are opticallyinterfered with each other to create an optical interference fringepattern P1, so that a refractive index grating P1 is recorded in therecording medium 10 due to the photorefractive effect.

The 0th-order beam of the signal beam 12 a (i.e., hologram-referencebeam) is scattered by the 0th-order-beam-scattering area SC of theincident-light-processing area R back to the recording medium 10.Therefore such scattered 0th-order beam of the signal beam 12 a isreferred to as “scattered-hologram-reference beam”. The diffraction beam(i.e., hologram-signal beam) of the signal beam 12 a is reflected by thediffraction-beam-processing area R2 of the incident-light-processingarea R back to enter the recording medium 10 as thereflected-hologram-signal beam.

The reflected-hologram-signal beam and the hologram-reference beam ofthe signal beam 12 a are optically interfered with each other in therecording medium 10 to create an optical interference fringe pattern P2,so that a refractive index grating P2 is recorded corresponding to theoptical interference fringe pattern P2 in the recording medium 10 due tothe photorefractive effect.

The scattered-hologram-reference beam and hologram-signal beam of thesignal beam 12 a are optically interfered with each other in therecording medium 10 to create an optical interference fringe pattern P3,so that a refractive index grating P3 is recorded in the recordingmedium 10 due to the photorefractive effect.

The scattered-hologram-reference beam and reflected-hologram-signal beamof the signal beam 12 a are optically interfered with each other in therecording medium 10 to create an optical interference fringe pattern P4,so that a refractive index grating P4 is recorded in the recordingmedium 10 due to the photorefractive effect.

Therefore, in the embodiment shown in FIG. 9, the refractive indexgratings P1, P2, P3 and P4 corresponding to optical interference fringepatterns P1, P2, P3 and P4 are hologram-recorded in the recording medium10 due to a photorefractive effect at least.

The reproducing process of the refractive index grating using the signalbeam 12 a (i.e., hologram-reference beam) in the recording medium 10will be hereinafter described.

The signal beam 12 a is not spatially modulated during the reproducingprocess because the spatial light modulator SLM displays the transparentpattern. Therefore no diffraction beam due to the spatial modulationoccurs and thus the signal beam 12 a includes only the 0th-order beam.

The recording medium 10 is illuminated with a signal beam 12 a (which isnot spatially modulated i.e., hologram-reference beam) with the samepositional and angular condition of the signal beam used in therecording. Just then, the refractive index gratings P1 and P2 areilluminated with the signal beam in the recording medium 10, so thatthere emanate a first reproduced wave from the refractive index gratingP1 corresponding to the recorded information and a second reproducedwave from the refractive index grating P2 respectively. Next the signalbeam 12 a (i.e., hologram-reference beam) is scattered by the0th-order-beam-scattering area SC of the incident-light-processing areaR back to the recording medium 10 and becomes ascattered-hologram-reference beam. Since the refractive index grating P3and the refractive index grating P4 in the recording medium 10 areilluminated with the scattered-hologram-reference beam, there emanate athird reproduced wave from the refractive index grating P3 correspondingto the recorded information and a fourth reproduced wave from therefractive index grating P4.

The scattered-hologram-reference beam goes out from the entrance surfaceof the recording medium 10, a part of which passes through the condenserlens 160. However, the scattered-hologram-reference beam is hardlyreceived by the photo detector 20 because of being scattered. Thisphenomenon contributes to simplification of the reproducing of therecorded information.

The first and third reproduced waves originated from the diffractionbeam component are reflected by the diffraction-beam-processing area R2of the incident-light-processing area R back to the recording medium 10and go out from the entrance surface of the recording medium 10 andpasses through the condenser lens 160. The second and fourth reproducedwaves originated from the diffraction beam component reflected by thediffraction-beam-processing area R2 in the recording process go out fromthe entrance surface of the recording medium 10 and passes through thecondenser lens 160. In this way, at least the first, second third andfourth reproduced waves go out from the entrance surface of therecording medium 10 and pass through the condenser lens 160. The laterprocesses are performed in the same manner of the embodiment shown inFIG. 3.

Third Embodiment

FIG. 10 shows a further modified example of the embodiment. Anincident-light-processing area comprises the diffraction-beam-processingarea R2 provided in the recording medium 10 on the opposite side of theentrance surface, and a 0th-order-beam-deflecting area RL providedinside the recording medium 10 along the track. The0th-order-beam-deflecting area RL has an inclined reflective surface fordeflecting the 0th-order beam of the signal beam 12 a to the inside withrespect to the axis of the signal beam 12 a. The0th-order-beam-deflecting area RL functions as another0th-order-beam-processing area R1 which separates the 0th-order beam ofthe incident light from the diffraction beam and returns a part of thebeam to the inside of the recording medium 10. The track-shaped0th-order-beam-deflecting area RL extending in the “y” direction returnsthe 0th-order beam of the signal beam 12 a to the recording medium 10,in the state of deflection toward one side of the track. The holographicrecording is carried out with the use of the interference fringescreated from the deflected 0th-order beam, the incident 0th-order beamand the incident diffraction beam and the reflected diffraction beam.According to the both modified examples described above, since all ofthe signal beam and the diffraction beam are returned to the inside ofthe recording medium 10, it is possible to efficiently use an amount ofilluminated light.

In other words, the incident-light-processing area R of the recordingmedium 10 comprises a 0th-order-beam-deflecting area RL deflecting the0th-order beam of the signal beam 12 a (i.e., hologram-reference beam)and a diffraction-beam-processing area R2 reflecting the diffractionbeam (i.e., hologram-signal beam). The 0th-order-beam-deflecting area RLcontinuously extends to a “y” direction of FIG. 10 like a track. Aplurality of 0th-order-beam-deflecting areas RL may be intermittentlyprovided in a line-like form. In this case, the0th-order-beam-deflecting areas RL can hold a positional information ofthe 0th-order-beam-processing area R1 in the recording medium 10.

The recording process of the refractive index grating using the signalbeam 12 a (i.e., hologram-reference beam and hologram-signal beam) inthe recording medium will be hereinafter described.

Since the recording medium 10 is illuminated with the signal beam 12 a,the hologram-reference beam and the hologram-signal beam are opticallyinterfered with each other to create an optical interference fringepattern P1, so that a refractive index grating P1 is recorded in therecording medium 10 due to the photorefractive effect.

The 0th-order beam of the signal beam 12 a (i.e., hologram-referencebeam) is deflected and reflected by the 0th-order-beam-deflecting areaRL of the incident-light-processing area R back to the recording medium10. Therefore such deflected and reflected 0th-order beam of the signalbeam 12 a is referred to as “deflected-hologram-reference beam”. Thediffraction beam (i.e., hologram-signal beam) of the signal beam 12 a isreflected by the diffraction-beam-processing area R2 of theincident-light-processing area R back to enter.

The reflected-hologram-signal beam and the hologram-reference beam ofthe signal beam 12 a are optically interfered with each other in therecording medium 10 to create an optical interference fringe pattern P2,so that a refractive index grating P2 is recorded corresponding to theoptical interference fringe pattern P2 in the recording medium 10 due tothe photorefractive effect.

The deflected-hologram-reference beam and hologram-signal beam of thesignal beam 12 a are optically interfered with each other in therecording medium 10 to create an optical interference fringe pattern P3,so that a refractive index grating P3 is recorded in the recordingmedium 10 due to the photorefractive effect.

The deflected-hologram-reference beam and reflected-hologram-signal beamof the signal beam 12 a are optically interfered with each other in therecording medium 10 to create an optical interference fringe pattern P4,so that a refractive index grating P4 is recorded in the recordingmedium 10 due to the photorefractive effect.

Therefore, in the embodiment shown in FIG. 10, the refractive indexgratings P1, P2, P3 and P4 corresponding to optical interference fringepatterns P1, P2, P3 and P4 are hologram-recorded in the recording medium10 due to a photorefractive effect at least.

The reproducing process of the refractive index grating using the signalbeam 12 a (i.e., hologram-reference beam) in the recording medium 10will be hereinafter described.

The signal beam 12 a is not spatially modulated during the reproducingprocess because the spatial light modulator SLM displays the transparentpattern. Therefore no diffraction beam due to the spatial modulationoccurs and thus the signal beam 12 a includes only the 0th-order beam.

The recording medium 10 is illuminated with a signal beam 12 a (which isnot spatially modulated i.e., hologram-reference beam) with the samepositional and angular condition of the signal beam used in therecording. Just then, the refractive index gratings P1 and P2 areilluminated with the signal beam in the recording medium 10, so thatthere emanate a first reproduced wave from the refractive index gratingP1 and a second reproduced wave from the refractive index grating P2respectively. Next the signal beam 12 a (i.e., hologram-reference beam)is deflected and reflected by the 0th-order-beam-deflecting area RL ofthe incident-light-processing area R back to the recording medium 10 andbecomes a deflected-hologram-reference beam. Since the refractive indexgrating P3 and the refractive index grating P4 in the recording medium10 are illuminated with the deflected-hologram-reference beam, thereemanate a third reproduced wave from the refractive index grating P3corresponding to the recorded information and a fourth reproduced wavefrom the refractive index grating P4.

The deflected-hologram-reference beam goes out from the entrance surfaceof the recording medium 10, a part of which passes through the condenserlens 160. Alternatively, a configuration preventing the beam fromreturning to the condenser lens 160 may be provided by a modifiedslanting angular shape of 0th-order-beam-deflecting area RL. Even if apart of the beam returns to the condenser lens 160, it is hardlyreceived by the photo detector 20 because of being deflected. Thisphenomenon contributes to simplification of the reproducing of therecorded information.

The first and third reproduced waves originated from the diffractionbeam component are reflected by the diffraction-beam-processing area R2of the incident-light-processing area R back to the recording medium 10and go out from the entrance surface of the recording medium 10 andpasses through the condenser lens 160. The second and fourth reproducedwaves originated from the diffraction beam component reflected by thediffraction-beam-processing area R2 in the recording process go out fromthe entrance surface of the recording medium 10 and passes through thecondenser lens 160. In this way, at least the first, second third andfourth reproduced waves go out from the entrance surface of therecording medium 10 and pass through the condenser lens 160. The laterprocesses are performed in the same manner of the embodiment shown inFIG. 3.

According to both the adjacent modified examples described above, sincethe 0th-order beam of the signal beam 12 a is returned to the inside ofthe recording medium 10 via the incident-light-processing area R, it ispossible to efficiently use an amount of illuminated light and furtherthese configurations contribute to simplification of the reproducing ofthe recorded information.

Fourth Embodiment

In the above embodiments, the holographic recording and producing in thereflective form in which the diffraction-beam-processing area R2 of theincident-light-processing area R reflects the light beam are described,but a transparent diffraction-beam-processing area R2 can also be usedwith the same effect in the present invention.

FIG. 11 shows a holographic recording and reproducing apparatusaccording to another embodiment that uses the recording medium having a0th-order-beam-processing area R1 and a diffraction-beam-processing areaR2 through which the light beam passes, i.e., the wholeincident-light-processing area R is light-permeable. The holographicrecording and reproducing apparatus of this embodiment is identical tothe apparatus shown in FIG. 1, except that the optical system composedof the beam splitter 13, the mirrors 18 and 19 for generating thereference beam is removed. The 0th-order-beam-processing area R1 may beadapted to a track used for a tracking servo as continuously extendingto a “y” direction of FIG. 11. The 0th-order-beam-processing area R1 isprovided by a processing configuration in that the0th-order-beam-processing area R1 differs from thediffraction-beam-processing area R2 in the transmissivity (orreflectivity or absorption coefficient) to separate the 0th-order beamfrom the diffraction beam.

In recording, as shown in FIGS. 11 and 12, the 0th-order beam and thediffraction beam of the signal beam 12 a itself from the spatial lightmodulator SLM interfere with each other in the recording medium 10 andgenerate a three-dimensional interference pattern.

Since the recording medium 10 is illuminated with the signal beam 12 a,the hologram-reference beam and the hologram-signal beam are opticallyinterfered with each other to create an optical interference fringepattern P1, so that a refractive index grating P1 is recorded in therecording medium 10 due to the photorefractive effect as shown in FIG.13.

The 0th-order beam (i.e., hologram-reference beam) of the signal beam 12a passes through the 0th-order-beam-processing area R1 of theincident-light-processing area R and also the diffraction beam (i.e.,hologram-signal beam) of the signal beam 12 a passes through thediffraction-beam-processing area R2 of the incident-light-processingarea R.

In reproducing, as shown in FIG. 14, the signal beam 12 a is notspatially modulated under the condition that the spatial light modulatorSLM displays the transparent pattern so as to include only the 0th-orderbeam (i.e., hologram-reference beam). With this hologram-reference beamthe recording medium 10 is illuminated under the same positional andangular condition of the signal beam used in the recording. Just then,the refractive index grating P1 is illuminated with the signal beam inthe recording medium 10, so that there emanates a first reproduced wavefrom the refractive index grating P1 corresponding to the recordedinformation. Since the signal beam 12 a is only the 0th-order beam, itgoes out from the opposite side of the entrance surface of the recordingmedium 10 on which the beam is incident and passes through the condenserlens 16 a. Also the first reproduced wave goes out from the oppositeside of the entrance surface of the recording medium 10 and passesthrough the condenser lens 16 a. Therefore the first reproduced wavegoes out from the opposite side of the entrance surface of the recordingmedium 10 and pass through the condenser lens 16 a at least in thereproducing process. The first reproduced wave constitutes to an imageformation of corresponding to the recorded information on the photodetector 20. Then the photoreceptor of the CCD 20 receives it tore-converted into the electrical digital data signals. Then, the digitaldata signals are sent to a decoder 26 to reproduce original data.

In the embodiment shown in FIG. 11, it is preferable that the recordingmedium 10 is made of a photo-sensitive material having a properties sothat the optical interference fringe pattern P1 emits a lot of lightamounts of the first reproduced wave to improve the precision ofreproduced recorded information. This is because the signal beam 12 a isreceived by the photoreceptor 20 at the same time.

Fifth Embodiment

FIG. 15 shows a still further modified example of the embodiment. Thepresent embodiment comprises a 0th-order-beam-scattering area SC forscattering only the 0th-order beam of the signal beam 12 a which isprovided inside the recording medium 10 on the opposite side of theentrance surface along the track (the “y” direction). The0th-order-beam-scattering area SC functions as the0th-order-beam-processing area R1 which separates the 0th-order beam ofthe incident light from the diffraction beam thereof and returns a partof the beam to the inside of the recording medium 10. The track-shaped0th-order-beam-scattering area SC extending in the “y” directionscatters the 0th-order beam of the signal beam 12 a back into therecording medium 10. The holographic recording is carried out with usingthe interference fringes created from the incident 0th-order beam, theincident diffraction beam and the scattered 0th-order beam.

In other words, the incident-light-processing area R of the recordingmedium 10 comprises a 0th-order-beam-scattering area SC scattering the0th-order beam of the signal beam 12 a (i.e., hologram-reference beam)and a diffraction-beam-processing area R2 allowing the diffraction beam(i.e., hologram-signal beam) to pass therethrough. The0th-order-beam-scattering area SC continuously extends to a “y”direction of FIG. 15 like a track. A plurality of0th-order-beam-scattering areas SC may be intermittently provided in aline-like form. In this case, the 0th-order-beam-scattering areas SC canhold a positional information of the 0th-order-beam-processing area R1in the recording medium 10.

The recording process of the refractive index grating using the signalbeam 12 a (i.e., hologram-reference beam and hologram-signal beam) inthe recording medium will be hereinafter described.

Since the recording medium 10 is illuminated with the signal beam 12 a,the hologram-reference beam and the hologram-signal beam are opticallyinterfered with each other to create an optical interference fringepattern P1, so that a refractive index grating P1 is recorded in therecording medium 10 due to the photorefractive effect.

The 0th-order beam of the signal beam 12 a (i.e., hologram-referencebeam) is scattered by the 0th-order-beam-scattering area SC of theincident-light-processing area R back to the recording medium 10 andbecomes a scattered-hologram-reference beam. The diffraction beam (i.e.,hologram-signal beam) of the signal beam 12 a passes through thediffraction-beam-processing area R2 of the incident-light-processingarea R and goes out from the opposite side of the entrance surface ofthe recording medium 10 on which the beam is incident.

The scattered-hologram-signal beam and the hologram-reference beam ofthe signal beam 12 a are optically interfered with each other in therecording medium 10 to create an optical interference fringe pattern P2,so that a refractive index grating P2 is recorded corresponding to theoptical interference fringe pattern P2 in the recording medium 10 due tothe photorefractive effect.

Therefore, in the embodiment shown in FIG. 15, at least the refractiveindex gratings P1 and P2 corresponding to optical interference fringepatterns P1 and P2 are hologram-recorded in the recording medium 10 dueto a photorefractive effect.

The reproducing process of the refractive index grating using the signalbeam 12 a (i.e., hologram-reference beam) in the recording medium 10will be hereinafter described.

The signal beam 12 a is not spatially modulated during the reproducingprocess because the spatial light modulator SLM displays the transparentpattern. Therefore the signal beam 12 a includes only the 0th-orderbeam.

With the signal beam 12 a (i.e., hologram-reference beam) the recordingmedium 10 is illuminated under the same positional and angular conditionof the signal beam used in the recording. Just then, the refractiveindex grating P1 is illuminated with the signal beam in the recordingmedium 10, so that there emanates a first reproduced wave from therefractive index grating P1 corresponding to the recorded information.

The 0th-order beam of the signal beam 12 a (i.e., hologram-referencebeam) is scattered by the 0th-order-beam-scattering area SC of theincident-light-processing area R back to the recording medium 10 andbecomes a scattered-hologram-reference beam. The refractive indexgrating P2 of the recording medium 10 is illuminated with thescattered-hologram-reference beam, so that there emanates a secondreproduced wave from the refractive index grating P2 corresponding tothe recorded information.

The first and second reproduced waves pass through thediffraction-beam-processing area R2 of the incident-light-processingarea R, and go out from the opposite side of the entrance surface of therecording medium 10 on which the beam is incident and passes through thecondenser lens 16 a. The later processes are performed in the samemanner of the embodiment shown in FIG. 14.

Since the scattered-hologram-reference beam goes out from the entrancesurface of the recording medium 10, the scattered-hologram-referencebeam is hardly received by the photo detector 20 because of beingscattered. This phenomenon contributes to simplification of thereproducing of the recorded information.

Sixth Embodiment

FIG. 16 shows a further modified example of the embodiment. A0th-order-beam-reflecting area RR which reflects only the 0th-order beamof the signal beam 12 a to the inside of the recording medium 10 may beprovided in the recording medium 10 on the opposite side of the entrancesurface along the track. The 0th-order-beam-reflecting area RR functionsas 0th-order-beam-processing area R1 which separates the 0th-order beamof the incident light from the diffraction beam thereof and returns apart of the beam to the inside of the recording medium 10. Thetrack-shaped 0th-order-beam-reflecting area RR extending in the “y”direction returns the 0th-order beam of the signal beam 12 a to thetrack of the recording medium 10 by reflection. The holographicrecording is carried out with using the interference fringes generatedfrom the 0th-order beam and the diffraction beam, and the reflected0th-order beam.

In other words, the incident-light-processing area R of the recordingmedium 10 comprises a 0th-order-beam-reflecting area RR reflecting the0th-order beam of the signal beam 12 a (i.e., hologram-reference beam)and a diffraction-beam-processing area R2 allowing the diffraction beam(i.e., hologram-signal beam) to pass therethrough. The0th-order-beam-reflecting area RR continuously extends to a “y”direction of FIG. 16 like a track. A plurality of0th-order-beam-reflecting areas RR may be intermittently provided in aline-like form. In this case, the 0th-order-beam-reflecting areas RR canhold a positional information of the 0th-order-beam-processing area R1in the recording medium 10.

The recording process of the refractive index grating using the signalbeam 12 a (i.e., hologram-reference beam and hologram-signal beam) inthe recording medium will be hereinafter described.

Since the recording medium 10 is illuminated with the signal beam 12 a,the hologram-reference beam and the hologram-signal beam are opticallyinterfered with each other to create an optical interference fringepattern P1, so that a refractive index grating P1 is recorded in therecording medium 10 due to the photorefractive effect.

The 0th-order beam of the signal beam 12 a (i.e., hologram-referencebeam) is reflected by the 0th-order-beam-reflecting area RR of theincident-light-processing area R back to the recording medium 10.Therefore such 0th-order beam of the signal beam 12 a reflected by the0th-order-beam-reflecting area RR is referred to as“reflected-hologram-reference beam”. The diffraction beam (i.e.,hologram-signal beam) of the signal beam 12 a passes through thediffraction-beam-processing area R2 of the incident-light-processingarea R and goes out from the opposite side of the entrance surface ofthe recording medium 10 on which the beam is incident.

The reflected-hologram-reference beam and the hologram-signal beam ofthe signal beam 12 a are optically interfered with each other in therecording medium 10 to create an optical interference fringe pattern P2,so that a refractive index grating P2 is recorded corresponding to theoptical interference fringe pattern P2 in the recording medium 10 due tothe photorefractive effect.

Therefore, in the embodiment shown in FIG. 16, at least the refractiveindex gratings. P1 and P2 corresponding to optical interference fringepatterns P1 and P2 are hologram-recorded in the recording medium 10 dueto a photorefractive effect.

The reproducing process of the refractive index grating using the signalbeam 12 a (i.e., hologram-reference beam) in the recording medium 10will be hereinafter described.

The signal beam 12 a is not spatially modulated during the reproducingprocess. Therefore no diffraction beam due to the spatial modulationoccurs and thus the signal beam 12 a includes only the 0th-order beam.

With the signal beam 12 a (i.e., hologram-reference beam) the recordingmedium 10 is illuminated under the same positional and angular conditionof the signal beam used in the recording. Just then, the refractiveindex grating P1 is illuminated with the signal beam in the recordingmedium 10, so that there emanates a first reproduced wave from therefractive index grating P1 corresponding to the recorded information.

Next the signal beam 12 a (i.e., hologram-reference beam) is reflectedby the 0th-order-beam-reflecting area RR of theincident-light-processing area R back to the recording medium 10 andbecomes a reflected-hologram-reference beam. The refractive indexgrating P2 of recording medium 10 is illuminated with thereflected-hologram-reference beam, so that there emanates a secondreproduced wave from the refractive index grating P2 corresponding tothe recorded information.

The first and second reproduced waves pass through thediffraction-beam-processing area R2 of the incident-light-processingarea R, and go out from the opposite side of the entrance surface of therecording medium 10 on which the beam is incident and passes through thecondenser lens 16 a. The later processes are performed in the samemanner of the embodiment shown in FIG. 14.

The reflected-hologram-reference beam goes out from the entrance surfaceof the recording medium 10, and can not reach the condenser lens 16 a.This phenomenon contributes to simplification of the reproducing of therecorded information.

Seventh Embodiment

FIG. 17 shows another modified example of the embodiment. The0th-order-beam-deflecting area RL which deflects the 0th-order beam ofthe signal beam 12 a to the inside of the recording medium 10 may beprovided in the recording medium 10 on the opposite side of the entrancesurface along the track. The 0th-order-beam-deflecting area RL extendingin the “y” direction reflectively returns the 0th-order beam of thesignal beam 12 a to the recording medium 10 while it deflects the0th-order beam to one side of the track. The holographic recording iscarried out with using the interference fringes generated from the0th-order beam, the diffraction beam, and the deflected 0th-order beam.According to these modified examples of the embodiment of the recordingand reproducing apparatuses, only the 0th-order beam of the signal beamis returned to the inside of the recording medium 10, so that it ispossible to efficiently use the amount of illuminated light.

In other words, the incident-light-processing area R of the recordingmedium 10 comprises a 0th-order-beam-deflecting area RL deflecting the0th-order beam of the signal beam 12 a (i.e., hologram-reference beam)and a diffraction-beam-processing area R2 allowing the diffraction beam(i.e., hologram-signal beam) to pass therethrough. The0th-order-beam-deflecting area RL continuously extends to a “y”direction of FIG. 17 like a track. A plurality of0th-order-beam-deflecting areas RL may be intermittently provided in aline-like form. In this case, the 0th-order-beam-deflecting areas RL canhold a positional information of the 0th-order-beam-processing area R1in the recording medium 10.

The recording process of the refractive index grating using the signalbeam 12 a (i.e., hologram-reference beam and hologram-signal beam) inthe recording medium will be hereinafter described.

Since the recording medium 10 is illuminated with the signal beam 12 a,the hologram-reference beam and the hologram-signal beam are opticallyinterfered with each other to create an optical interference fringepattern P1, so that a refractive index grating P1 is recorded in therecording medium 10 due to the photorefractive effect.

The 0th-order beam of the signal beam 12 a (i.e., hologram-referencebeam) is deflected and reflected by the 0th-order-beam-deflecting areaRL of the incident-light-processing area R back to the recording medium10 and becomes a deflected-hologram-reference beam. The diffraction beam(i.e., hologram-signal beam) of the signal beam 12 a passes through thediffraction-beam-processing area R2 of the incident-light-processingarea R and goes out from the opposite side of the entrance surface ofthe recording medium 10 on which the beam is incident.

The deflected-hologram-reference beam and the hologram-reference beam ofthe signal beam 12 a are optically interfered with each other in therecording medium 10 to create an optical interference fringe pattern P2,so that a refractive index grating P2 is recorded corresponding to theoptical interference fringe pattern P2 in the recording medium 10 due tothe photorefractive effect.

Therefore, in the embodiment shown in FIG. 17, the refractive indexgratings P1 and P2 corresponding to optical interference fringe patternsP1 and P2 are hologram-recorded in the recording medium 10 due to aphotorefractive effect at least.

The reproducing process of the refractive index grating using the signalbeam 12 a (i.e., hologram-reference beam) in the recording medium 10will be hereinafter described.

The signal beam 12 a is not spatially modulated during the reproducingprocess. Therefore no diffraction beam due to the spatial modulationoccurs and thus the signal beam 12 a includes only the 0th-order beam.

With the signal beam 12 a (i.e., hologram-reference beam) the recordingmedium 10 is illuminated under the same positional and angular conditionof the signal beam used in the recording. Just then, the refractiveindex grating P1 is illuminated with the signal beam in the recordingmedium 10, so that there emanates a first reproduced wave from therefractive index grating P1 corresponding to the recorded information.

Next the 0th-order beam of the signal beam 12 a (i.e.,hologram-reference beam) is deflected by the 0th-order-beam-deflectingarea RL of the incident-light-processing area R back to the recordingmedium 10 and becomes a deflected-hologram-reference beam. Therefractive index grating P2 of recording medium 10 is illuminated withthe deflected-hologram-reference beam, so that there emanates a secondreproduced wave from the refractive index grating P2 corresponding tothe recorded information.

The first and second reproduced waves pass through thediffraction-beam-processing area R2 of the incident-light-processingarea R, and go out from the opposite side of the entrance surface of therecording medium 10 on which the beam is incident and pass through thecondenser lens 16 a. The later processes are performed in the samemanner of the embodiment shown in FIG. 14.

The deflected-hologram-reference beam goes out from the entrance surfaceof the recording medium 10, and can not reach the condenser lens 16 a.This phenomenon contributes to simplification of the reproducing of therecorded information.

According to these modified examples described above, since only the0th-order beam of the signal beam 12 a is returned to the inside of therecording medium 10 via the incident-light-processing area R, it ispossible to efficiently use an amount of illuminated light and furtherthese configurations contribute to simplification of the reproducing ofthe recorded information.

Eighth Embodiment

In the above embodiments, the holographic recording and producing in theform in which the incident-light-processing area R is integrallyprovided in the recording medium 10 are described, but theincident-light-processing area R may be provided to the apparatus withthe same advantageous effect in the present invention.

FIG. 18 shows a holographic recording and reproducing apparatusaccording to another embodiment that uses another recording medium. Theholographic recording and reproducing apparatus comprises anincident-light-processing area R which is disposed on or adjacent to therecording medium 10 at an opposite side of an entrance surface thereofon which the signal beam is incident. The incident-light-processing areaR separates the 0th-order beam and the diffraction beam from each otherto return a part of the incident beam to the inside of the recordingmedium. The incident-light-processing area R comprises a0th-order-beam-processing area R1 for passing the 0th-order beam in thesignal beam 12 a and a diffraction-beam-processing area R2 forreflecting the diffraction beam in the signal beam 12 a. As far as theprocessing function of the 0th-order-beam-processing area R1 isdifferent from that of the diffraction-beam-processing area R2, the0th-order-beam-processing area R1 may have a function to absorb the0th-order beam. The 0th-order-beam-processing area R1 may have alight-permeability or light-absorbency. The holographic recording andreproducing apparatus shown in FIG. 18 is identical to the apparatusshown in FIG. 3, except that the incident-light-processing area R isprovided in the apparatus adjacent to the recording medium 10.

As shown in FIG. 19, in the apparatus, the incident-light-processingarea R is disposed at the opposite side of an entrance surface of therecording medium 10 and has as a window of the 0th-order-beam-processingarea R1 for passing the 0th-order beam in the signal beam 12 atherethrough. The recording medium 10 is relatively disposed so as to bemovable in a “y” direction of the Figure with respect to the window ofthe 0th-order-beam-processing area R1. The recording medium 10 ismovably disposed so as to move in the direction D_(TR) making apredetermined angle of θ (θ≠0) with an extending direction D_(SLM) of arow or a column of the spatial light modulator SLM pixel matrix.

As shown in FIG. 20, the diffraction beam becomes the highest frequencycomponent in the signal beam 12 a modulated by the spatial lightmodulator SLM on the basis of pixel matrix (pitch is “a”) thereof. Thesignal beam 12 a is Fourier-transformed through the condenser lens 160and then the spectrum distribution of light intensity with respect to aspatial frequency appears in the Fourier plane FF, as shown in FIG. 20,according to the spatial modulation due to the spatial light modulatorSLM.

The process of recording and reproducing of hologram of this embodimentis identical to the apparatus case shown in FIG. 3, except that theincident-light-processing area R and the recording medium 10 arerelatively moved.

Ninth Embodiment

Furthermore FIG. 21 shows another modified embodiment. Instead of thetransparent portion of the 0th-order-beam-processing area, there isprovided a 0th-order-beam-scattering area SC in theincident-light-processing area R on the opposite side of the entrancesurface of the recording medium 10. The holographic recording is carriedout with the use of the interference fringes created from the 0th-orderbeam, the diffraction beam, the scattered 0th-order beam and thereflected diffraction beam.

Tenth Embodiment

FIG. 22 shows a further modified example of the embodiment. There isprovided a 0th-order-beam-deflecting area RL in theincident-light-processing area R on or adjacent to the opposite side ofthe entrance. The 0th-order-beam-deflecting area RL has an inclinedreflective surface for deflecting the 0th-order beam of the signal beam12 a to the inside with respect to the axis of the signal beam 12 a. The0th-order-beam-deflecting area RL functions as another0th-order-beam-processing area R1 which separates the 0th-order beam ofthe incident light from the diffraction beam and returns a part of thebeam to the inside of the recording medium 10. The holographic recordingis carried out with the use of the interference fringes generated fromthe 0th-order beam, the diffraction beam, the deflected 0th-order beamand the reflected diffraction beam.

Eleventh Embodiment

FIG. 23 shows a still further holographic recording and reproducingapparatus according to another embodiment that uses a transparentdiffraction-beam-processing area R2 through which the light beam passesin the incident-light-processing area R. This holographic recording andreproducing apparatus is identical to the apparatus shown in FIG. 1,except that the incident-light-processing area R is added and theoptical system composed of the beam splitter 13, the mirrors 18 and 19for generating the reference beam is removed. In addition, theincident-light-processing area R comprises a 0th-order-beam-scatteringarea SC scattering the 0th-order beam and a transparent portion T(diffraction-beam-processing area R2) allowing the diffraction beam topass therethrough.

As shown in FIG. 24, in the apparatus at the opposite side of theentrance surface of the recording medium 10, there is a0th-order-beam-scattering area SC provided inside of theincident-light-processing area R which separates the 0th-order beam ofthe incident light from the diffraction beam thereof and returns a partof the beam to the inside of the recording medium 10. The0th-order-beam-scattering area SC scatters only the 0th-order beam ofthe signal beam 12 a. The track-shaped 0th-order-beam-scattering area SCextending in the “y” direction scatters the 0th-order beam of the signalbeam 12 a back into the recording medium 10. The holographic recordingis carried out with the use of the interference fringes generated fromthe 0th-order beam, the diffraction beam, the scattered 0th-order beamand the reflected diffraction beam to generate optical interferencefringe patterns, so that refractive index gratings are recorded in therecording medium 10 due to the photorefractive effect. In reproducing,the recording medium 10 is fixed in the apparatus in the same manner inthe recording and illuminated with the a converged reference beam 12.When the reference beam 12 passes through the recording medium 10, thena reproduced wave is outputed from the refractive index grating of therecording medium 10. When the reference beam 12 is incident thenreproduced beam which reproduces the recorded light interference patternappears on the opposite side of the recording medium 10. Leading thereproduced wave to an inverse Fourier transform lens 16 a and performingthe inverse Fourier transform reproduces the dot pattern signals. Thedot pattern signals are received by a photo detector 20 such as acharge-coupled device CCD and the like disposed in the position of afocal length, and re-converted into the electrical digital data signals.Then, the digital data signals are sent to a decoder to reproduceoriginal data.

Twelfth Embodiment

FIG. 25 shows a part of another further modified embodiment. Thisholographic recording and reproducing apparatus is identical to theapparatus shown in FIG. 23, except that the 0th-order-beam-reflectingarea RR which reflects only the 0th-order beam of the signal beam 12 ainside and a transparent portion T (diffraction-beam-processing area R2)allowing the diffraction beam to pass therethrough are provided in theapparatus.

In other words, the incident-light-processing area R adjacent to therecording medium 10 comprises a 0th-order-beam-reflecting area RRreflecting the 0th-order beam of the signal beam 12 a (i.e.,hologram-reference beam) and a diffraction-beam-processing area R2allowing the diffraction beam (i.e., hologram-signal beam) to passtherethrough.

Thirteenth Embodiment

FIG. 26 shows a part of a further modified embodiment. This holographicrecording and reproducing apparatus is identical to the apparatus shownin FIG. 23, except the 0th-order-beam-deflecting area RL which reflectsonly the 0th-order beam of the signal beam 12 a inside and a transparentportion T (diffraction-beam-processing area R2) allowing the diffractionbeam to pass therethrough are provided in the apparatus. The0th-order-beam-deflecting area RL of the incident-light-processing areaextending in the “y” direction of the Figure deflects the 0th-order beamtoward one side of the track inside the recording medium 10 so that theholographic recording is carried out with the use of the interferencefringes generated from the 0th-order beam, the diffraction beam and thedeflected 0th-order beam. The 0th-order-beam-deflecting area RL has aninclined reflective surface with respect to the axis of the signal beam12 a for deflecting the 0th-order beam of the signal beam 12 a to theinside. The 0th-order-beam-deflecting area RL functions as another0th-order-beam-processing area R1 which separates the 0th-order beam ofthe incident light from the diffraction beam and returns a part of thebeam to the inside of the recording medium 10. The track-shaped0th-order-beam-deflecting area RL extending in the “y” direction returnsthe 0th-order beam of the signal beam 12 a to the recording medium 10deflecting toward one side of the track. The holographic recording iscarried out with the use of the interference fringes generated from the0th-order beam, the diffraction beam, the deflected 0th-order beam andthe reflected diffraction beam.

These modified examples have configurations to return only the 0th orderbeam of the signal beam to the inside of the recording medium 10, sothat it is possible to efficiently use an amount of illuminated light.The incident-light-processing area has a function to separate theincident beam to return a part thereof to the inside of the recordingmedium in order to individually process the 0th-order beam and thediffraction beam in the incident light with different processes.Therefore the incident-light-processing area may have a0th-order-beam-processing area allowing the 0th-order beam to passthrough or absorbing the 0th-order beam; and adiffraction-beam-reflecting area reflecting or deflecting or scatteringthe diffraction-beam. Alternatively the incident-light-processing areamay have a 0th-order-beam-processing area reflecting or scattering ordeflecting or absorbing the 0th-order beam; and adiffraction-beam-reflecting area reflecting or deflecting thediffraction-beam.

Fourteenth Embodiment

FIG. 27 shows a part of a still further modified embodiment incomparison with the apparatus shown in FIG. 18 in that theincident-light-processing area R is individually provided adjacent tothe recording medium 10. As shown in FIG. 27, theincident-light-processing area R and the condenser lens 160 may beintegrally fixed on a support case Rsu to face each other so that therecording medium 10 is able to be inserted therebetween.

Fifteenth Embodiment

Furthermore, according to another embodiment of the present invention,the recording medium 10 may be provided in a disk or card form. Forexample, a cartridge CR shown in FIG. 28 accommodates a disk of therecording medium 10 to be rotatable. The cartridge CR is provided withthe incident-light-processing areas R at the inner sidewall thereof andhas an opening for access to the recording medium disk with the lightbeam.

Sixteenth Embodiment

In addition to the above embodiments of the holographic recording andreproducing method and the apparatus therefor, the present inventionapparently includes a recording method, a reproducing method, arecording apparatus, and a reproducing apparatus of the hologram. In theabove embodiments, the laser beam is spatially modulated in accordancewith the two-dimensional data, in other words, two-dimensionalmodulation is used. The present invention, however, is applicable to aholographic recording and reproducing method and apparatus whichspatially modulate the laser beam in accordance with one-dimensionaldata. In the above embodiments, the photorefractive material is used forthe photosensitive material of the recording medium, but otherphotosensitive materials such as hole burning material, photochromicmaterial and the like may be used for the photosensitive material of therecording medium.

1. A method for holographic recording and reproducing comprising arecording process and a reproducing process, the recording processincluding the steps of: generating a signal beam by spatially modulatinga coherent reference beam in accordance with information to be recorded;illuminating with the signal beam a recording medium made of aphotosensitive material to allow the signal beam to pass through saidrecording medium; and creating a diffraction grating area recorded by alight interference pattern in a portion where a 0th-order beam and adiffraction beam of the signal beam interfere with each other insidesaid recording medium; and the reproducing process including the stepof: illuminating said diffraction grating area with said reference beamto generate a reproduced wave corresponding to the signal beam.
 2. Themethod for holographic recording and reproducing according to claim 1,further comprising an incident-light-processing area provided in saidrecording medium on an opposite side of an entrance surface of therecording medium on which the signal beam is incident, theincident-light-processing area separating the 0th-order beam and thediffraction beam from each other to return a part of the incident beamto the inside of said recording medium.
 3. The method for holographicrecording and reproducing according to claim 2, further comprising aline-like track formed in a part of said incident-light-processing area.4. The method for holographic recording and reproducing according toclaim 3, wherein said track has positioning information of saidincident-light-processing area with respect to said recording medium. 5.The method for holographic recording and reproducing according to claim2, wherein said incident-light-processing area comprises a0th-order-beam-processing area and a diffraction-beam-reflecting area,the 0th-order-beam-processing area allowing the 0th-order beam to passthrough or scattering the 0th-order beam or deflecting the 0th-orderbeam or absorbing the 0th-order beam, the diffraction-beam-reflectingarea defining the 0th-order-beam-processing area and reflecting thediffraction beam.
 6. The method for holographic recording andreproducing according to claim 2, wherein said incident-light-processingarea comprises a 0th-order-beam-processing area and adiffraction-beam-reflecting area, the 0th-order-beam-processing areareflecting the 0th-order beam or scattering the 0th-order beam ordeflecting the 0th-order beam or absorbing the 0th-order beam, thediffraction-beam-reflecting area defining the 0th-order-beam-processingarea and allowing the diffraction beam to pass through.
 7. The methodfor holographic recording and reproducing according to claim 2, whereinsaid incident-light-processing area comprises a0th-order-beam-processing area and a diffraction-beam-reflecting area,the 0th-order-beam-processing area reflecting the 0th-order beam orscattering the 0th-order beam or deflecting the 0th-order beam orallowing the 0th-order beam to pass through, thediffraction-beam-reflecting area defining the 0th-order-beam-processingarea and absorbing the diffraction beam.
 8. The method for holographicrecording and reproducing according to claim 5, further comprising aspatial light modulator including a rows and columns matrix of pixels tospatially modulate the reference beam, wherein said spatial lightmodulator and said recording medium are relatively disposed in such amanner that said 0th-order-beam-processing area is not illuminated withthe diffraction beam of the signal beam.
 9. The method for holographicrecording and reproducing according to claim 8, wherein said spatiallight modulator and said recording medium are relatively disposed withrespect to an optical axis of the signal beam in such a manner that anextending direction of a row or a column of said spatial light modulatormakes a predetermined angle of θ (θ≠0) with an extending direction ofsaid 0th-order-beam-processing area.
 10. The method for holographicrecording and reproducing according to claim 6, wherein the reproducedwave is output from the opposite side of the entrance surface of therecording medium on which the signal beam is incident, in thereproducing process.
 11. A method for holographic recording comprising:generating a signal beam by spatially modulating a coherent referencebeam in accordance with information to be recorded; illuminating withthe signal beam a recording medium made of a photosensitive material toallow the signal beam to pass through said recording medium; andcreating a diffraction grating area recorded by a light interferencepattern in a portion where a 0th-order beam and a diffraction beam ofthe signal beam interfere with each other inside said recording medium.12. The method for recording a hologram according to claim 11, furthercomprising an incident-light-processing area provided in said recordingmedium on an opposite side of an entrance surface of the recordingmedium on which the signal beam is incident, theincident-light-processing area separating the 0th-order beam and thediffraction beam from each other to return a part of the incident beamto the inside of said recording medium.
 13. The method for recording ahologram according to claim 12, further comprising a line-like trackformed in a part of said incident-light-processing area.
 14. The methodfor recording a hologram according to claim 13, wherein said track haspositioning information of said incident-light-processing area withrespect to said recording medium.
 15. The method for recording ahologram according to claim 12, wherein said incident-light-processingarea comprises a 0th-order-beam-processing area and adiffraction-beam-reflecting area, the 0th-order-beam-processing areaallowing the 0th-order beam to pass through or scattering the 0th-orderbeam or deflecting the 0th-order beam or absorbing the 0th-order beam,the diffraction-beam-reflecting area defining the0th-order-beam-processing area and reflecting the diffraction beam. 16.The method for recording a hologram according to claim 12, wherein saidincident-light-processing area comprises a 0th-order-beam-processingarea and a diffraction-beam-reflecting area, the0th-order-beam-processing area reflecting the 0th-order beam orscattering the 0th-order beam or deflecting the 0th-order beam orabsorbing the 0th-order beam, the diffraction-beam-reflecting areadefining the 0th-order-beam-processing area and allowing the diffractionbeam to pass through.
 17. The method for recording a hologram accordingto claim 12, wherein said incident-light-processing area comprises a0th-order-beam-processing area and a diffraction-beam-reflecting area,the 0th-order-beam-processing area reflecting the 0th-order beam orscattering the 0th-order beam or deflecting the 0th-order beam orallowing the 0th-order beam to pass through, thediffraction-beam-reflecting area defining the 0th-order-beam-processingarea and absorbing the diffraction beam.
 18. The method for recording ahologram according to claim 15, further comprising a spatial lightmodulator including a rows and columns matrix of pixels to spatiallymodulate the reference beam, wherein said spatial light modulator andsaid recording medium are relatively disposed in such a manner that said0th-order-beam-processing area is not illuminated with the diffractionbeam of the signal beam.
 19. The method for recording a hologramaccording to claim 18, wherein said spatial light modulator and saidrecording medium are relatively disposed with respect to an optical axisof the signal beam in such a manner that an extending direction of a rowor a column of said spatial light modulator makes a predetermined angleof θ (θ≠0) with an extending direction of said 0th-order-beam-processingarea.
 20. A method for holographic reproducing comprising: providing arecording medium made of a photosensitive material having a diffractiongrating area formed through a recording process including the steps of:generating a signal beam by spatially modulating a coherent referencebeam in accordance with information to be recorded; and illuminatingwith the signal beam the recording medium to allow the signal beam topass through said recording medium so as to form the diffraction gratingarea recorded by a light interference pattern in a portion where a0th-order beam and a diffraction beam of the signal beam interfere witheach other inside said recording medium; and illuminating a coherentreference beam to the diffraction grating area to generate a reproducedwave corresponding to the signal beam.
 21. The method for reproducing ahologram according to claim 20, further comprising anincident-light-processing area provided in said recording medium on anopposite side of an entrance surface of the recording medium on whichthe signal beam is incident, the incident-light-processing areaseparating the 0th-order beam and the diffraction beam from each otherto return a part of the incident beam to the inside of said recordingmedium.
 22. The method for reproducing a hologram according to claim 21,further comprising a line-like track formed in a part of saidincident-light-processing area.
 23. The method for reproducing ahologram according to claim 22, wherein said track has positioninginformation of said incident-light-processing area with respect to saidrecording medium.
 24. The method for reproducing a hologram according toclaim 21, wherein said incident-light-processing area comprises a0th-order-beam-processing area and a diffraction-beam-reflecting area,the 0th-order-beam-processing area allowing the 0th-order beam to passthrough or scattering the 0th-order beam or deflecting the 0th-orderbeam or absorbing the 0th-order beam, the diffraction-beam-reflectingarea defining the 0th-order-beam-processing area and reflecting thediffraction beam.
 25. The method for reproducing a hologram according toclaim 21, wherein said incident-light-processing area comprises a0th-order-beam-processing area and a diffraction-beam-reflecting area,the 0th-order-beam-processing area reflecting the 0th-order beam orscattering the 0th-order beam or deflecting the 0th-order beam orabsorbing the 0th-order beam, the diffraction-beam-reflecting areadefining the 0th-order-beam-processing area and allowing the diffractionbeam to pass through.
 26. The method for reproducing a hologramaccording to claim 21, wherein said incident-light-processing areacomprises a 0th-order-beam-processing area and adiffraction-beam-reflecting area, the 0th-order-beam-processing areareflecting the 0th-order beam or scattering the 0th-order beam ordeflecting the 0th-order beam or allowing the 0th-order beam to passthrough, the diffraction-beam-reflecting area defining the0th-order-beam-processing area and absorbing the diffraction beam. 27.The method for reproducing a hologram according to claim 24, wherein thediffraction grating area of the recording medium is recorded by using aspatial light modulator including a rows and columns matrix of pixels insuch a manner that said spatial light modulator and said recordingmedium are relatively disposed so that said 0th-order-beam-processingarea is not illuminated with the diffraction beam of the signal beam.28. The method for reproducing a hologram according to claim 27, whereinsaid spatial light modulator and said recording medium are relativelydisposed with respect to an optical axis of the signal beam in such amanner that an extending direction of a row or a column of said spatiallight modulator makes a predetermined angle of θ (θ≠0) with an extendingdirection of said 0th-order-beam-processing area.
 29. The method forreproducing a hologram according to claim 25, wherein the reproducedwave is output from the opposite side of the entrance surface of therecording medium on which the signal beam is incident, in thereproducing process.
 30. A holographic recording and reproducingapparatus for recording information as a diffraction grating area in arecording medium, and for reproducing said recorded information fromsaid diffraction grating area, said holographic recording andreproducing apparatus comprising: a holding section for detachablyholding a recording medium made of a photosensitive material; a lightsource for generating a coherent reference beam; a signal beamgenerating unit including a spatial light modulator, said spatial lightmodulator spatially modulating said reference beam in accordance withsaid information to be recorded to generate a signal beam; aninterference unit including an illuminating optical system forilluminating the recording medium with the signal beam to allow it toenter into and pass through said recording medium, said illuminatingoptical system creating a diffraction grating area according to a lightinterference pattern in a portion where a 0th-order beam and adiffraction beam of the signal beam interfere with each other insidesaid recording medium, and said illuminating optical system illuminatingsaid diffraction grating area with said reference beam to generate areproduced wave corresponding to the signal beam; and a detecting unitfor detecting said recorded information formed into an image by thereproduced wave.
 31. The holographic recording and reproducing apparatusaccording to claim 30, further comprising an incident-light-processingarea provided in said recording medium on an opposite side of anentrance surface of the recording medium on which the signal beam isincident, the incident-light-processing area separating the 0th-orderbeam and the diffraction beam from each other to return a part of theincident beam to the inside of said recording medium.
 32. Theholographic recording and reproducing apparatus according to claim 31,further comprising a line-like track formed in a part of saidincident-light-processing area.
 33. The holographic recording andreproducing apparatus according to claim 32, wherein said track haspositioning information of said incident-light-processing area withrespect to said recording medium.
 34. The holographic recording andreproducing apparatus according to claim 31, wherein saidincident-light-processing area comprises a 0th-order-beam-processingarea and a diffraction-beam-reflecting area, the0th-order-beam-processing area allowing the 0th-order beam to passthrough or scattering the 0th-order beam or deflecting the 0th-orderbeam or absorbing the 0th-order beam, the diffraction-beam-reflectingarea defining the 0th-order-beam-processing area and reflecting thediffraction beam.
 35. The holographic recording and reproducingapparatus according to claim 31, wherein said incident-light-processingarea comprises a 0th-order-beam-processing area and adiffraction-beam-reflecting area, the 0th-order-beam-processing areareflecting the 0th-order beam or scattering the 0th-order beam ordeflecting the 0th-order beam or absorbing the 0th-order beam, thediffraction-beam-reflecting area defining the 0th-order-beam-processingarea and allowing the diffraction beam to pass through.
 36. Theholographic recording and reproducing apparatus according to claim 31,wherein said incident-light-processing area comprises a0th-order-beam-processing area and a diffraction-beam-reflecting area,the 0th-order-beam-processing area reflecting the 0th-order beam orscattering the 0th-order beam or deflecting the 0th-order beam orallowing the 0th-order beam to pass through, thediffraction-beam-reflecting area defining the 0th-order-beam-processingarea and absorbing the diffraction beam.
 37. The holographic recordingand reproducing apparatus according to claim 34, further comprising aspatial light modulator including a rows and columns matrix of pixels tospatially modulate the reference beam, wherein said spatial lightmodulator and said recording medium are relatively disposed in such amanner that said 0th-order-beam-processing area is not illuminated withthe diffraction beam of the signal beam.
 38. The holographic recordingand reproducing apparatus according to claim 37, wherein said spatiallight modulator and said recording medium are relatively disposed withrespect to an optical axis of the signal beam in such a manner that anextending direction of a row or a column of said spatial light modulatormakes a predetermined angle of θ (θ≠0) with an extending direction ofsaid 0th-order-beam-processing area.
 39. The holographic recording andreproducing apparatus according to claim 35, wherein the reproduced waveis output from the opposite side of the entrance surface of therecording medium on which the signal beam is incident.
 40. Theholographic recording and reproducing apparatus according to claim 34,further comprising a splitting unit separating the reproduced wave froman optical path of the reference beam.
 41. A holographic recordingapparatus for recording information as a diffraction grating area in arecording medium, comprising: a holding section for detachably holding arecording medium made of a photosensitive material; a light source forgenerating a coherent reference beam; a signal beam generating unitincluding a spatial light modulator, said spatial light modulatorspatially modulating said reference beam in accordance with saidinformation to be recorded to generate a signal beam; and aninterference unit including an illuminating optical system forilluminating the recording medium with the signal beam to allow it toenter into and pass through said recording medium, said illuminatingoptical system creating a diffraction grating area according to a lightinterference pattern in a portion where a 0th-order beam and adiffraction beam of the signal beam interfere with each other insidesaid recording medium.
 42. The holographic recording apparatus accordingto claim 41, wherein the recording medium comprises anincident-light-processing area provided in said recording medium on anopposite side of an entrance surface of the recording medium on whichthe signal beam is incident, the incident-light-processing areaseparating the 0th-order beam and the diffraction beam from each otherto return a part of the incident beam to the inside of said recordingmedium.
 43. The holographic recording apparatus according to claim 42,further comprising a line-like track formed in a part of saidincident-light-processing area.
 44. The holographic recording apparatusaccording to claim 43, wherein said track has positioning information ofsaid incident-light-processing area with respect to said recordingmedium.
 45. The holographic recording apparatus according to claim 42,wherein said incident-light-processing area comprises a0th-order-beam-processing area and a diffraction-beam-reflecting area,the 0th-order-beam processing area allowing the 0th-order beam to passthrough or scattering the 0th-order beam or deflecting the 0th-orderbeam or absorbing the 0th-order beam, the diffraction-beam-reflectingarea defining the 0th-order-beam-processing area and reflecting thediffraction beam.
 46. The holographic recording apparatus according toclaim 42, wherein said incident-light-processing area comprises a0th-order-beam-processing area and a diffraction-beam-reflecting area,the 0th-order-beam-processing area reflecting the 0th-order beam orscattering the 0th-order beam or deflecting the 0th-order beam orabsorbing the 0th-order beam, the diffraction-beam-reflecting areadefining the 0th-order-beam-processing area and allowing the diffractionbeam to pass through.
 47. The holographic recording apparatus accordingto claim 42, wherein said incident-light-processing area comprises a0th-order-beam-processing area and a diffraction-beam-reflecting area,the 0th-order-beam-processing area reflecting the 0th-order beam orscattering the 0th-order beam or deflecting the 0th-order beam orallowing the 0th-order beam to pass through, thediffraction-beam-reflecting area defining the 0th-order-beam-processingarea and absorbing the diffraction beam.
 48. The holographic recordingapparatus according to claim 45, further comprising a spatial lightmodulator including a rows and columns matrix of pixels to spatiallymodulate the reference beam, wherein said spatial light modulator andsaid recording medium are relatively disposed in such a manner that said0th-order-beam-processing area is not illuminated with the diffractionbeam of the signal beam.
 49. The holographic recording apparatusaccording to claim 48, wherein said spatial light modulator and saidrecording medium are relatively disposed with respect to an optical axisof the signal beam in such a manner that an extending direction of a rowor a column of said spatial light modulator makes a predetermined angleof θ (θ≠0) with an extending direction of said 0th-order-beam-processingarea.
 50. A holographic reproducing apparatus for reproducinginformation recorded as a diffraction grating area in a recordingmedium, the reproducing apparatus comprising: a holding section fordetachably holding a recording medium made of a photosensitive material;a light source for generating a coherent reference beam; an illuminatingunit including an illuminating optical system for illuminating therecording medium with the reference beam to allow it to enter into andpass through the diffraction grating area in the recording medium togenerate a reproduced wave corresponding to the signal beam; and adetecting unit for detecting said recorded information formed into animage by the reproduced wave.
 51. The holographic reproducing apparatusaccording to claim 50, wherein the recording medium comprises anincident-light-processing area provided in said recording medium on anopposite side of an entrance surface of the recording medium on whichthe signal beam is incident, the incident-light-processing areaseparating the 0th-order beam and the diffraction beam from each otherto return a part of the incident beam to the inside of said recordingmedium.
 52. The holographic reproducing apparatus according to claim 51,further comprising a line-like track formed in a part of saidincident-light-processing area.
 53. The holographic reproducingapparatus according to claim 52, wherein said track has positioninginformation of said incident-light-processing area with respect to saidrecording medium.
 54. The holographic reproducing apparatus according toclaim 51, wherein said incident-light-processing area comprises a0th-order-beam-processing area and a diffraction-beam-reflecting area,the 0th-order-beam-processing area allowing the 0th-order beam to passthrough or scattering the 0th-order beam or deflecting the 0th-orderbeam or absorbing the 0th-order beam, the diffraction-beam-reflectingarea defining the 0th-order-beam-processing area and reflecting thediffraction beam.
 55. The holographic reproducing apparatus according toclaim 51, wherein said incident-light-processing area comprises a0th-order-beam-processing area and a diffraction-beam-reflecting area,the 0th-order-beam-processing area reflecting the 0th-order beam orscattering the 0th-order beam or deflecting the 0th-order beam orabsorbing the 0th-order beam, the diffraction-beam-reflecting areadefining the 0th-order-beam-processing area and allowing the diffractionbeam to pass through.
 56. The holographic reproducing apparatusaccording to claim 51, wherein said incident-light-processing areacomprises a 0th-order-beam-processing area and adiffraction-beam-reflecting area, the 0th-order-beam-processing areareflecting the 0th-order beam or scattering the 0th-order beam ordeflecting the 0th-order beam or allowing the 0th-order beam to passthrough, the diffraction-beam-reflecting area defining the0th-order-beam-processing area and absorbing the diffraction beam. 57.The holographic reproducing apparatus according to claim 54, wherein thediffraction grating area of the recording medium is recorded by using aspatial light modulator including a rows and columns matrix of pixels insuch a manner that said spatial light modulator and said recordingmedium are relatively disposed so that said 0th-order-beam-processingarea is not illuminated with the diffraction beam of the signal beam.58. The holographic reproducing apparatus according to claim 57, whereinsaid spatial light modulator and said recording medium are relativelydisposed with respect to an optical axis of the signal beam in such amanner that an extending direction of a row or a column of said spatiallight modulator makes a predetermined angle of θ (θ≠0) with an extendingdirection of said 0th-order-beam-processing area.
 59. The holographicreproducing apparatus according to claim 55, wherein the reproduced waveis output from the opposite side of the entrance surface of therecording medium on which the signal beam is incident.
 60. Theholographic reproducing apparatus according to claim 54, furthercomprising a splitting unit separating the reproduced wave from anoptical path of the reference beam.
 61. A recording medium made of aphotosensitive material capable of being recorded by illumination with acoherent light beam, comprising an incident-light-processing areaprovided in said recording medium on an opposite side of an entrancesurface of the recording medium on which the light beam is incident, theincident-light-processing area separating a 0th-order beam and adiffraction beam of the light beam from each other to return a part ofthe incident beam to the inside of said recording medium.
 62. Therecording medium according to claim 61, further comprising a line-liketrack formed in a part of said incident-light-processing area.
 63. Therecording medium according to claim 62, wherein said track haspositioning information of said incident-light-processing area withrespect to said recording medium.
 64. The recording medium according toclaim 61, wherein said incident-light-processing area comprises a0th-order-beam-processing area and a diffraction-beam-reflecting area,the 0th-order-beam-processing area allowing the 0th-order beam to passthrough or scattering the 0th-order beam or deflecting the 0th-orderbeam or absorbing the 0th-order beam, the diffraction-beam-reflectingarea defining the 0th-order-beam-processing area and reflecting thediffraction beam.
 65. The recording medium according to claim 61,wherein said incident-light-processing area comprises a0th-order-beam-processing area and a diffraction-beam-reflecting area,the 0th-order-beam-processing area reflecting the 0th-order beam orscattering the 0th-order beam or deflecting the 0th-order beam orabsorbing the 0th-order beam, the diffraction-beam-reflecting areadefining the 0th-order-beam-processing area and allowing the diffractionbeam to pass through.
 66. The recording medium according to claim 61,wherein said incident-light-processing area comprises a0th-order-beam-processing area and a diffraction-beam-reflecting area,the 0th-order-beam-processing area reflecting the 0th-order beam orscattering the 0th-order beam or deflecting the 0th-order beam orallowing the 0th-order beam to pass through, thediffraction-beam-reflecting area defining the 0th-order-beam-processingarea and absorbing the diffraction beam.
 67. A holographic recording andreproducing apparatus for recording information as a diffraction gratingarea in a recording medium, and for reproducing said recordedinformation from said diffraction grating area, said holographicrecording and reproducing apparatus comprising: a holding section fordetachably holding a recording medium made of a photosensitive material;a light source for generating a coherent reference beam; a signal beamgenerating unit including a spatial light modulator, said spatial lightmodulator spatially modulating said reference beam in accordance withsaid information to be recorded to generate a signal beam; aninterference unit including an illuminating optical system forilluminating the recording medium with the signal beam to allow it toenter into and pass through said recording medium, said illuminatingoptical system creating a diffraction grating area according to a lightinterference pattern in a portion where a 0th-order beam and adiffraction beam of the signal beam interfere with each other insidesaid recording medium, and said illuminating optical system illuminatingsaid diffraction grating area with said reference beam to generate areproduced wave corresponding to the signal beam; anincident-light-processing area provided adjacent to an opposite side ofan entrance surface of the recording medium on which the signal beam isincident, the incident-light-processing area separating the 0th-orderbeam and the diffraction beam from each other to return a part of theincident beam to the inside of said recording medium; and a detectingunit for detecting said recorded information formed into an image by thereproduced wave.
 68. The holographic recording and reproducing apparatusaccording to claim 67, wherein said incident-light-processing areacomprises a 0th-order-beam-processing area and adiffraction-beam-reflecting area, the 0th-order-beam-processing areaallowing the 0th-order beam to pass through or scattering the 0th-orderbeam or deflecting the 0th-order beam or absorbing the 0th-order beam,the diffraction-beam-reflecting area defining the0th-order-beam-processing area and reflecting the diffraction beam. 69.The holographic recording and reproducing apparatus according to claim67, wherein said incident-light-processing area comprises a0th-order-beam-processing area and a diffraction-beam-reflecting area,the 0th-order-beam-processing area reflecting the 0th-order beam orscattering the 0th-order beam or deflecting the 0th-order beam orabsorbing the 0th-order beam, the diffraction-beam-reflecting areadefining the 0th-order-beam-processing area and allowing the diffractionbeam to pass through.
 70. The holographic recording and reproducingapparatus according to claim 67, wherein said incident-light-processingarea comprises a 0th-order-beam-processing area and adiffraction-beam-reflecting area, the 0th-order-beam-processing areareflecting the 0th-order beam or scattering the 0th-order beam ordeflecting the 0th-order beam or allowing the 0th-order beam to passthrough, the diffraction-beam-reflecting area defining the 0th-orderbeam-processing area and absorbing the diffraction beam.
 71. Theholographic recording and reproducing apparatus according to claim 67,wherein said spatial light modulator includes a rows and columns matrixof pixels and wherein said spatial light modulator and said recordingmedium are relatively disposed with respect to an optical axis of thesignal beam in such a manner that an extending direction of a row or acolumn of said spatial light modulator makes a predetermined angle of θ(θ≠0) with an extending direction of said 0th-order-beam-processingarea.
 72. The holographic recording and reproducing apparatus accordingto claim 69, wherein the reproduced wave is output from the oppositeside of the entrance surface of the recording medium on which the signalbeam is incident.
 73. The holographic recording and reproducingapparatus according to claim 68, further comprising a splitting unitseparating the reproduced wave from an optical path of the referencebeam.
 74. A holographic recording apparatus for recording information asa diffraction grating area in a recording medium, comprising: a holdingsection for detachably holding a recording medium made of aphotosensitive material; a light source for generating a coherentreference beam; a signal beam generating unit including a spatial lightmodulator, said spatial light modulator spatially modulating saidreference beam in accordance with said information to be recorded togenerate a signal beam; an interference unit including an illuminatingoptical system for illuminating the recording medium with the signalbeam to allow it to enter into and pass through said recording medium,said illuminating optical system creating a diffraction grating areaaccording to a light interference pattern in a portion where a 0th-orderbeam and a diffraction beam of the signal beam interfere with each otherinside said recording medium; and an incident-light-processing areaprovided adjacent to an opposite side of an entrance surface of therecording medium on which the signal beam is incident, theincident-light-processing area separating the 0th-order beam and thediffraction beam from each other to return a part of the incident beamto the inside of said recording medium.
 75. The holographic recordingapparatus according to claim 74, wherein said incident-light-processingarea comprises a 0th-order-beam-processing area and adiffraction-beam-reflecting area, the 0th-order-beam-processing areaallowing the 0th-order beam to pass through or scattering the 0th-orderbeam or deflecting the 0th-order beam or absorbing the 0th-order beam,the diffraction-beam-reflecting area defining the0th-order-beam-processing area and reflecting the diffraction beam. 76.The holographic recording apparatus according to claim 74, wherein saidincident-light-processing area comprises a 0th-order-beam-processingarea and a diffraction-beam-reflecting area, the0th-order-beam-processing area reflecting the 0th-order beam orscattering the 0th-order beam or deflecting the 0th-order beam orabsorbing the 0th-order beam, the diffraction-beam-reflecting areadefining the 0th-order-beam-processing area and allowing the diffractionbeam to pass through.
 77. The holographic recording apparatus accordingto claim 74, wherein said incident-light-processing area comprises a0th-order-beam-processing area and a diffraction-beam-reflecting area,the 0th-order-beam-processing area reflecting the 0th-order beam orscattering the 0th-order beam or deflecting the 0th-order beam orallowing the 0th-order beam to pass through, thediffraction-beam-reflecting area defining the 0th-order-beam-processingarea and absorbing the diffraction beam.
 78. The holographic recordingapparatus according to claim 74, wherein said spatial light modulatorincludes a rows and columns matrix of pixels and wherein said spatiallight modulator and said recording medium are relatively disposed withrespect to an optical axis of the signal beam in such a manner that anextending direction of a row or a column of said spatial light modulatormakes a predetermined angle of θ (θ≠0) with an extending direction ofsaid 0th-order-beam-processing area.
 79. A holographic reproducingapparatus for reproducing information recorded as a diffraction gratingarea in a recording medium, the reproducing apparatus comprising: aholding section for detachably holding a recording medium made of aphotosensitive material; a light source for generating a coherentreference beam; an illuminating unit including an illuminating opticalsystem for illuminating the recording medium with the reference beam toallow it to enter into and pass through the diffraction grating area inthe recording medium to generate a reproduced wave corresponding to thesignal beam; an incident-light-processing area provided adjacent to anopposite side of an entrance surface of the recording medium on whichthe signal beam is incident, the incident-light-processing areaseparating the 0th-order beam and the diffraction beam from each otherto return a part of the incident beam to the inside of said recordingmedium; and a detecting unit for detecting said recorded informationformed into an image by the reproduced wave.
 80. The holographicreproducing apparatus according to claim 79, wherein saidincident-light-processing area comprises a 0th-order-beam-processingarea and a diffraction-beam-reflecting area, the0th-order-beam-processing area allowing the 0th-order beam to passthrough or scattering the 0th-order beam or deflecting the 0th-orderbeam or absorbing the 0th-order beam, the diffraction-beam-reflectingarea defining the 0th-order-beam-processing area and reflecting thediffraction beam.
 81. The holographic reproducing apparatus according toclaim 79, wherein said incident-light-processing area comprises a0th-order-beam-processing area and a diffraction-beam-reflecting area,the 0th-order-beam-processing area reflecting the 0th-order beam orscattering the 0th-order beam or deflecting the 0th-order beam orabsorbing the 0th-order beam, the diffraction-beam-reflecting areadefining the 0th-order-beam-processing area and allowing the diffractionbeam to pass through.
 82. The holographic reproducing apparatusaccording to claim 79, wherein said incident-light-processing areacomprises a 0th-order-beam-processing area and adiffraction-beam-reflecting area, the 0th-order-beam-processing areareflecting the 0th-order beam or scattering the 0th-order beam ordeflecting the 0th-order beam or allowing the 0th-order beam to passthrough, the diffraction-beam-reflecting area defining the0th-order-beam-processing area and absorbing the diffraction beam. 83.The holographic reproducing apparatus according to claim 80, wherein thediffraction grating area of the recording medium is recorded by using aspatial light modulator including a rows and columns matrix of pixels insuch a manner that said spatial light modulator and said recordingmedium are relatively disposed so that said 0th-order-beam-processingarea is not illuminated with the diffraction beam of the signal beam.84. The holographic reproducing apparatus according to claim 83, whereinsaid spatial light modulator and said recording medium are relativelydisposed with respect to an optical axis of the signal beam in such amanner that an extending direction of a row or a column of said spatiallight modulator makes a predetermined angle of θ (θ≠0) with an extendingdirection of said 0th-order-beam-processing area.
 85. The holographicreproducing apparatus according to claim 81, wherein the reproduced waveis output from the opposite side of the entrance surface of therecording medium on which the signal beam is incident, in thereproducing process.
 86. The holographic reproducing apparatus accordingto claim 80, further comprising a splitting unit separating thereproduced wave from an optical path of the reference beam.